been expended for pure research in anthropology under one direction as during the past year; and praise and honour are due to the business men forming the directory of the Exposition in Chicago, who have so cordially met my proposals and furnished the means for carrying them out on so grand a scale. Notwithstanding the vast material interests involved in the Columbian Exposition, it must be admitted that Chicago has nobly supported pure science in this connection and has shown an appreciation of its high aims.

On the Honduras Expedition Prof. Putnam reports as follows:

It was stated in the last report that an expedition had just started to make the preliminary explorations for the ancient ruins of Copan, and in that report is given a brief outline of the origin and plans of this undertaking on the part of the Museum to be carried on by the assistance of patrons of archæological research. It is indeed a pleasurable duty to announce that the first season's work of the expedition has proved a decided success; and that although the party had many trials and difficulties to overcome, no serious accidents or sickness occurred. Messrs. Saville and Owens returned in safety, in May last, bringing with them a large number of most interesting and important objects illustrating the wonderful carvings in stone; several vessels and many fragments of pottery; numerous ornaments made of stone, shells and bone; stone implements; and portions of human skeletons. Among the latter are several incisor teeth, each of which contains a small piece of green stone, presumbly jadeite, set in a cavity drilled on the front surface of the tooth. We had before received from very ancient graves in Yucatan human teeth filed in a peculiar manner, and now we have teeth from the ancient graves in Copan ornamented in another way. This is of particular interest in adding one more to the several facts pointing to Asiatic arts and customs as the origin of those of the early peoples of Central America. A most striking resemblance to Asiatic art is noticed in several of the heads carved in stone,-one in particular, if seen in any collection and not labelled as to its origin, would probably pass almost unchallenged as from Southern Asia. These may prove to be simply coincidences of expression of peoples of corresponding mental development brought about by corresponding natural surroundings and conditions. At present we must admit that there are many resemblances in architecture, sculpture, ornament, and religious symbolism, between Central America and portions of Asia. The true meaning of these resemblances will be made known as authentic materials for study are obtained by such thorough and exhaustive field work as the Museum has been carrying on; and none is so important for this special subject as that of the Honduras expedition. For this work, however, a large sum of money is required. The ten years allowed for the work in Honduras by the edict of that government must be utilised to the fullest extent; and each year must find the Museum ready to put its party in the field well equipped and provided with money for the very expensive work to be performed.

It is not my intention to give an abstract of the results of last year's explorations at Copan. It is far better that the report should be carefully prepared by those engaged in the actual field work from year to year. After sufficient information has been obtained about the ruins themselves, and the architectural and chronological relationship of the various structures; and after a thorough knowledge of the different modes of burial has been acquired, and all possible objects have been collected, then conclusions can be drawn which will be of scientific value, since they will be based on a thorough knowledge of all the facts. An important beginning was made by the expedition last year, plans of the plaza and of the principal structures forming the great mass of the ruins having been made, many photographs taken, and paper moulds of important sculptures, lines of hieroglyphs and several of the large idols or carved monoliths secured. Considering the difficulties of transportation (wholly by mules to the coast-a seven days' journey), both Messrs. Saville and Owens, and all associated with them must be congratulated on what they accomplished. Since the return of the expedition the photographs have been printed, preliminary reports have been prepared, and casts have been made from the moulds. These casts are now being placed in the Museum, and a series has also been made for the Boston Art Museum, and another for the Columbian Exposition.

UNIVERSITY AND EDUCATIONAL
INTELLIGENCE.

CAMBRIDGE.-Prof. Liveing announces a course of demonstr tions in spectroscopic chemistry, to be given during the fr three weeks of the Easter term, daily (except on Saturdays; & 11, beginning on April 24.

The examination in Sanitary Science for the Diploma i Public Health will be held from April 4 to April 8.

The honorary degree of Doctor in Science will be confere! on Prof. Virchow, at a special congregation on Tuesday, March 21.

Scholars' Fund to H. Woods, of St. John's College, for the A grant of £65 has been made from the Worts Travelling purpose of paleontological research in Saxony and Bohemia Lawrence Crawford, B. A., Fifth Wrangler, 1890, has bee elected to a Fellowship at King's College.

SOCIETIES AND ACADEMIES.
LONDON.

Royal Society, February 16.-"The Value of the Mechanical Equivalent of Heat, deduced from some Exper ments performed with the view of establishing the Relation between the Electrical and Mechanical Units, together with an Investigation into the Capacity for Heat of Water at differen Temperatures." By E. H. Griffiths, M. A., Assistant Lecturer, Sidney Sussex College, Cambridge, assisted by G. M. Clara, B. A., Sidney Sussex College, Cambridge. Communicated by R. T. Glazebrook, F.R.S.

If a calorimeter is suspended in a chamber, the walls of which are maintained at a constant temperature, we can, by observa tions over a small range across that outside temperature, deda the rate of rise due to the mechanical work done in the calori meter, when the supply of heat is derived from stirring only By repeating the observations in a similar manner over ranges whose mean temperature 0, differs from that of the surroundi walls 00, we obtain the change in temperature due to the com bined effects of the stirring, radiation, conduction, and convre tion at all points of our whole range of temperature. As the success of the method depends (1) on the possibility of ma taining the exterior temperature unchanged, and (2) on the regularity of the supply of heat due to the stirring, we brie indicate our method of securing those conditions.

1. The calorimeter was suspended within an air-tight stee chamber. The walls and floor of this chamber were doch: and the space between them filled with mercury. The whit structure was placed in a tank containing about 20 gallons water, and was supported in such a manner that there were about 3 inches of water both above and beneath it. The mercury was connected by a tube with a gas regulator of a nove form, which controlled the supply of gas to a large number jets. Above those jets was placed a flat silver tube, throug which tap water was continually flowing into the tank, all part of which were maintained at an equal temperature by the r rotation of a large screw. Thus, the calorimeter may be t garded as suspended within a chamber placed in the bulb a huge thermometer-the mercury in that bulb weighing 70 A change of 1° C. in the temperature of the tank water case the mercury in the tubes of the regulating apparatus to rise abus 300 mm. Special arrangements were made by which it possible to set the apparatus so that the walls surrounding the calorimeter could be maintained for any length of time at required temperature, from that of the tap water (in suame about 13° C. in winter 3° C.) up to 40° C. or 50°C. We by observation that the temperature of the steel chamber ( once adjusted) did not vary by 1/500° C., and we believe variations were much less.

2. We experienced great difficulty in devising a suitable is of stirrer; and we attribute the failure of our earlier expence to defects in the ordinary forms. We find it impossible, out a lengthy description, to give a clear idea of the stirrer mately adopted. We can only state here that it was comple immersed when the depth of the water exceeded 1 cm,

1 The calorimeter was of cylindrical form, and suspended by tre tubes. It was made of "gilding metal," which both internally ternally was covered with a considerable thickness of gold Al surfaces within the calorimeter were thickly gilded.

its bearings were outside the steel chamber, and that the water was thrown from the bottom to the lid of the calorimeter.

More than 100 experiments were performed (many of them lasting several hours) in order to determine the value of σ + p (@2 −01), when the calorimeter contained different masses of water. The harmony amongst the results was satisfactory.

The pressure in the space between the calorimeter and the walls of the steel chamber was reduced, as a rule, to between 0.3 and 10 mm.

The absolute value of the loss by radiation, &c., at different pressures was ascertained, and it was found that the rate of gain or loss decreased very rapidly when the pressure was reduced below 0.5 mm.

over different ranges we can find without previously obtaining J; or, having obtained f, we can find wx and g, and then by equation (4) deduce the value of J from a single experiment. We have adopted both methods as a check upon the calculations, which involve much arithmetic. The latter method is the more convenient, as it enables us to ascertain the results of separate experiments, but it cannot be applied until the values of f, 8, and we have previously been obtained by observations on two different weights at two different temperatures. We give the values of T at 15°, 20°, and 25° C.

TABLE XLI.-VALUES OF T AT 15°, 20°, AND 25° C.

25

558'09 740'75 459'81

58155

703'20

δε J.R'.M'

(2)

where R' is the resistance of the coil, and M' the capacity for heat of the calorimeter and its contents at a temperature 01

Throughout the experiments E was kept constant, the arrangement for maintaining the ends of the coil at a constant potential difference worked admirably, and it is probable that in no case did the variations exceed 1/10,000 of the mean potential difference during each experiment.

The value of R was determined by a direct comparison (conducted by Mr. Glazebrook) with the B. A. standards and values of R were expressed in true ohms as defined in the B. A. Report, 1892.

The difference between the temperature of the coil and that of the surrounding water was ascertained, and the resulting difference of resistance was found to be such that &R='00422n2, where # was the number of Clark cells by which the potential difference at the end of the coil was maintained.

The mercury thermometers were standardised by direct comparison with several platinum thermometers, and a further comparison has (through the kindness of Dr. Guillaume) been made with the Paris hydrogen standard. The difference obtained by the two methods in the value of the range is only *005° C.

The various quantities in equation (2) having been determined (with the exception of J and M'), we can deduce from equation (2) the time (T) of rising 1°C at any point of our range when R = 1 and E is the potential difference of one Clark cell at 15° C.

No of col. J

This value of J, as previously pointed out (equation 5), is entirely independent of the value assigned to the water equivalent of the calorimeter.

And we find the water equivalent of the calorimeter at 15° C. in terms of water at 15° C. 85*340 grams. The water equivalent of the calorimeter at 25 C. in terms of water at 15° C. 86.174 grams. Hence water equivalent

=

=

85 3400'000977(t

15).

We can now find the capacity for heat of the calorimeter and contents for any weight of water at 15°, 20°, and 25° C., and deduce the value of J from each group separately.

TABLE XLIII.-VALUES OF J.

hence

0); 0) + wx (1 + g01 = T

Group.!

By repeating observations with different weights of water, w and w, and observing T, and T2, the corresponding times, we obtain by subtraction

J

12(21⁄2 - W1) (1 + f0, − 0) = T1 T2 . . . (5)

Hence when @1 = (ie. at the standard temperature) we can find J without first ascertaining the values of f, g, or the water equivalent of the calorimeter, and by repeating the observations 1 = rise in temperature per 1 second due to the stirring. P = gain or loss in temperature per 1 second due to radiation, &c., when 01-061 C.

2 The pressures were ascertained by a McLeod's gauge.

We have in the above table given the values resulting from the calculation at different temperatures, for the limit of our experimental errors is thus clearly indicated, since the values of

1 Over the range 14" to 26° C.

Jought (in the absence of experimental errors) to be identical at all temperatures. The close agreement between the values from different groups, and from the same group at different temperatures, is a satisfactory proof of the accuracy of our determination of the water equivalents of the calorimeter, and of the changes in it and in the capacity for heat of the water. Hence, if we assume

1. The unit of resistance as defined in the "B. A. Report," 1892;

2. That the E. M. F. of the Cavendish Standard Clark cell at 15° C. = 1'4342 volts;

1

=

3. That the thermal unit quantity of heat required to raise I gram of water through 1o C. at 15° C., the most probable value of

J = 778 99 foot-pounds per thermal unit F in latitude of Greenwich (g 32.195).

=

The length of this abstract is already unduly great, and we will, therefore, not enter on any discussion of the results beyond remarking that if we express Rowland's value of J in terms of our thermal unit we exceed his value by I part in 930, and we exceed the mean of Joule's determination by I part in 350.3

The difference between Rowland's value of the temperature coefficient of the specific heat of water and ours would, however, cause both his and our values of J to be identical if expressed in terms of athermal unit at 11'5° C.

March 2.-"The Effects of Mechanical Stress on the Electrical Resistance of Metals." By James H. Gray, M. A., B. Sc., and James B. Henderson, B. Sc., International Exhibition Scholars, Glasgow University. Communicated by Lord Kelvin,

P.R.S.

This investigation was begun for the purpose of obtaining an easily worked method of testing the effect of any mechanical treatment on the density and specific resistance of metals.

For alteration of density, copper, lead, and manganese copper wires were tested. The effect of stretching was always to diminish the density, the alteration being small however: for copper about per cent., and for lead per cent. The effect of drawing through holes in a steel plate was somewhat greater, showing at first an increase of 2 per cent. ; and, when the drawing was continued, the density began to diminish till, after drawing from diameter 2 mm. to 13 mm., it showed an increase on its original value of per cent. Several other interesting results on alteration of density were obtained.

The most important part of the investigation, however, relates to the alteration of specific resistance of copper, iron, and steel wire due to stretching; and, in connection with this, the authors wish particularly to emphasise the advantages to be gained from using the unit of specific resistance introduced by Weber, who always defined it in weight measure, that is, as the resistance of a length of the metal numerically equal to its density and section unity.

The conclusions arrived at are that for practical purposes any mechanical treatment, however severe, does not affect the electrical properties of the metals tested. As contrasted with this, it is interesting to note that the smallest impurity in the metal produces a greater change than the most severe chanical treatment. For example, an impurity of per cent. lowers the electrical conductivity by 13'5 per cent., while an impurity of per cent. lowers it as much as 30 per cent.

me

"A New Hypothesis concerning Vision." By John Berry Haycraft, M.D., D. Sc. Communicated by E. A. Schäfer, F. R. S. The author pointed out that when a blue pigment is mixed with its complementary pigment-orange-yellow-it makes a grey, not a green as is generally stated. This can be shown by the use of transparent colours, such as watery solutions of the 1 If we assume the E. M. F. of our Clark cells to be the same as that of the Cavendish standard (and we are inclined to think we have over-estimated the difference), we get J=4'1930 X 107.

2 The value obtained by us in 1891 = (4192 +) x 107.

3 Rowland obtained the mean value of Joule's determinations by assigning values to different experiments, and the above comparison refers to the numbers thus obtained. If, however, we attach equal weight to all Joule's results, as reduced by Rowland, the mean exceeds our value by 1 in 4280, assuming our expression for the temperature coefficient of the specific heat of water.

aniline dyes. When you mix an opaque oil blue with its com plementary orange-yellew and get a green it is because the ligh only passes through a very thin superficial film of the mixture and a paint which is orange-yellow in the mass is only a pa: yellow in a thin film, and transmits the green spectral r stopped by the orange-yellow. In this case, therefore, the thin film of paint which alone affects the light is not a mixture blue and its complementary orange yellow, but only a mixture of blue and pale yellow.

In the case of Maxwell's colour discs you get a grey if the blue and yellow are complementary, or a green c red if they are not, just as in the case of mixtures of transparent pigments. Complementary pigments are simp those which between them absorb all spectral rays; thus bize absorbs red, yellow, and some green, and the complementary orange-yellow absorbs violet, blue, and some green. A mixture of these pigments on the palette-if transparent enough-or o the Maxwell's disc absorbs, therefore, the light which falls upur it from all parts of the spectrum in about equal proportions. examined by the spectroscope the mixture of pigments and the rotating disc both give a dim, unbroken spectrum identical wi that of white paper held in half light. In our study of vistat we have to deal with the stimulus-spectral rays-and the resulting sensations. Inasmuch as the stimulus-the light of : dim, unbroken spectrum-is the same whether the eye locks a a mixture of blue and orange yellow on a palette, at a Maxwel's disc, or again at a piece of white paper held in half light, the resulting sensation must in all cases be the same-we call it grey white. In the case of the rotating Maxwell's disc experiment we not dealing with the fusion of blue and orange-yellow sensations but the adding together of two halves of the spectrum to mast a whole one. Once understood, the physiologist will disar the experiment altogether, as it has no bearing upon col vision.

The work of Sprengel, Darwin, and especially of Sir !}Lubbock, shows that the colour sense has gradually been evolve. by the coloured environment of the species. We may infer that in the ancestral condition in which light was distinguished tr darkness, but blue was undistinguishable say from red, all visi stimuli were felt as white or various shades of grey. The greate the amount of spectral light the nearer the sensation approache white. This, if accepted, explains why the outer and less use parts of the retina are colour blind in the human eye at the pre sent day, and further explains why a minimal stimulus from: coloured object gives rise to a sensation grey. Just as we an smell something, but require to "sniff,' in order to make ou what it is, so the coloured object held far away may give ne only to the primitive sensation grey, and has to be brought nearer in order that its colour quality can be felt.

We may explain the fact that an artificial mixture of spect green and red gives rise to the sensation yellow by the fact that coloured objects which send to the eye red and green rays send the intermediate yellow; these objects give rise to the ser tion yellow, and we call them by that name. Inasmuch as association of red and green rays has in the evolution of the eve always combined with yellow rays to produce the sensa yellow, we can explain, as an instance of association, the far that artificially combined red and green rays produce a ye. * sensation.

When, say, red and blue-green spectral rays are artifica combined, they produce a grey sensation, and this we explain by the fact that no fully coloured natural object sen to the eye such a combination, which combination, therefore played no part in the evolution of the colour sense, and i produces merely a primitive sensation of simple brightness-.:

or grey.

That a coloured object brightly illuminated appears whe follows the law of maximal stimulation, for in this c the object absorbs so slight a proportion of the light from one part of the spectrum that that part gives rise to its ma effect, and the rest of the spectrum can do no more. In case, therefore, the eye is affected equally (maximally) by all r of the spectrum, and we have of course the sensation of white

The above view is an attempt to explain some of the fac vision by showing that they are on all fours with other e known to the physiologist. This seems to the author a scientific method than the one adopted by Young and Helm who "conceive" a visual apparatus, and endow it with s properties as will, in their opinion, account for the facts of vi sensation.

Chemical Society, February 16.-Prof. A. Crum Brown, F.R.S., President, in the chair. It was announced that the following changes in the Council were proposed by the Council for the ensuing year :-President, Prof. H. E. Armstrong, vice Prof. Crum Brown. Vice-Presidents: Dr. E. Atkinson and Mr. C. O'Sullivan, vice Prof. Hartley and Mr. Warington. Secretary, Prof. Dunstan, vice Prof. Armstrong. Ordinary Members of the Council: Messrs. C. F. Cross, Bernard Dyer, Lazarus Fletcher, and W. A. Shenstone, vice Mr. H. Bassett, Prof. Ferguson, Mr. J. Heron, and Mr. S. U. Pickering.-The following papers were read: Note on the preparation of platinous chloride, and on the interaction of chlorine and mercury, by W. A. Shenstone and C. R. Beck. The authors find that very pure specimens of chlorine may be prepared by igniting platinous chloride obtained by heating hydrogen platinichloride in a current of dry hydrogen chloride. On passing the dry gas for fifteen hours over the platinichloride at the boiling point of mercury and igniting the residue in vacuo, chlorine was obtained which contained 99 84 per cent. of the gas. A portion of the platinous chloride obtained in this experiment was heated at 500° in a current of dry hydrogen chloride during many hours; on then igniting the residue, chlorine was evolved which when treated with mercury only left a residue of o'06 per cent. unabsorbed. The platinous chloride made by the above method probably contain a little platinum, but as a source of chlorine, it seems to be superior to the product of more familiar processes. The second sample of chlorine mentioned above acted very sluggishly on mercury; this fact, considered in connection with the great purity of the gas, supports the authors' view that the activity of chlorine towards mercury is probably due to the presence of impurity in the former.-The action of phosphoric anhydride on fatty acids. Part III., by F. S. Kipping. In the present paper the author shows that caprylone (C-H15)CO, nonylone (C,H17)2CO, and myristone (C13H27)2CO, can be readily prepared from the corresponding fatty acids by the action of phosphoric anhydride; a number of derivatives of these ketones are described. Mixed ketones of the general formula R.CO.R' are produced when a mixture of two fatty acids is treated with phosphoric anhydride at a moderately high temperature; the mixed ketone is, however, accompanied by two simple ketones. Treatment with phosphoric anhydride would seem to be one of the simplest and most rapid methods by which the ketone (CH2n+1)CO can be prepared from a fatty acid CHO. -Regularities in the melting points of certain paraffinoid compounds of similar constitution, by F. S. Kipping. The author has prepared and characterised a number of hydroximes, secondary alcohols and ethereal salts derived from the fatty ketones (CnH2n+1)2CO and draws attention to certain regularities observed on comparing the melting points of these compounds. The melting points of all ketones of the general formula CHO cannot be calculated by means of the formula given by Mills (Phil. Mag. 1884), inasmuch as isomeric ketones frequently melt at different between temperatures. Some relations constitution and physical constants in the case of benzenoid amines, by W. R. Hodgkinson and L. Limpach. A study of the formyl and acetyl derivatives of certain homologues of aniline shows, (1) that the entry of alkyl groups into the nucleus affects the melting and boiling points in a regular manner; (2) that the conversion of formyl into acetyl also involves an alteration in physical properties in extent the same as that produced by introducing CH, into the nucleus in an ortho- or para-position relatively to the amido-group, and (3) that the same (or any?) alkyl group entering the nucleus in the meta-positions has no effect on melting or boiling point. Several numerical regularities are also apparent. -Electrolysis of sodic ethylic camphorate, by J. Walker. On electrolysis, sodium ethyl camphorate yields the ethyl salts of two new acids, viz. campholytic acid, CH COOH, and camphotetic acid, C16H2,(COOH)2. The first of these is a monabasic, unsaturated acid boiling at 240-242°. It is lævo-rotatory, but gives a dextro-rotatory ethyl salt. Camphotetic acid is a colourless crystalline solid, melting at 132°; it behaves as a saturated, bibasic acid and forms well-characterised salts. Judging from the nature of the electrolysis and the behaviour of campholytic acid towards bromine, camphoric acid should contain the group

HC. COOH

-C. COOH

28

-The hydrates of hydrogen chloride, by S. U. Pickering. Determinations of the densities of aqueous solutions of hydrogen chloride show a strongly-marked break indicative of the presence of a trihydrate. The author has obtained this hydrate in the solid state by making a series of freezing point determinations; it forms large, transparent crystals melting at 24°9. The densities also indicate the existence of a change of curvature at a point corresponding to a hexhydrate; the freezing-point determinations afford no evidence for or against the existence of this substance, but the presence of a decahydrate was indicated. -A new base from Corydalis cava, by J. A. Dobbie and A. Lauder. By exhausting crude corydaline with hot water the authors have isolated a new alkaloid of the composition C19H25 NO, which they term corytuberine; this alkaloid contains only two methoxy-groups, whilst corydaline contains four. A number of its salts are described. The authors also give some notes on yet another alkaloid, which they consider to be distinct from all the bases of Corydalis cava hitherto described. February 20.-Lord Playfair, F. R.S., Vice-President, in the chair. This being the anniversary of the death of Hermann Kopp, Prof. T. E. Thorpe delivered a memorial lecture entitled "The Life Work of Hermann Kopp."

PARIS.

Academy of Sciences, March 6.-M. Loewy in the chair. -On a partial differential equation, by Émile Picard. On the spectro-photographic method which makes it possible to obtain photographs of the chromosphere, faculæ, protuberances, &c., by M. J. Janssen. This method was outlined by M. Janssen as early as 1869, at the Exeter meeting of the British Association.Analysis of the ashes of the diamond, by M. Henri Moissan. All the specimens of the carbonado and Cape diamond analysed contained iron, as shown by the potassium sulphocyanide reaction. This metal formed the larger portion of the ashes. Silicium also occurred regularly, and calcium very frequently. It will be remembered that this alkaline earthy metal was found by M. Daubrée in native iron from Ovifak.-On some new properties of the diamond, by M. Henri Moissan (see Notes). The pancreas and the nervous centres controlling the glycemic function, by MM. A. Chauveau and M. Kaufmann. The inhibitory action exerted by the pancreas on the glycogenic function of the liver appears to be dependent upon an excito-secretory centre controlling the cells performing the internal secretion of the pancreas. This centre is situated in the encephalic portion of the spinal cord, and the inhibitory impulse acts through this centre upon an excito-secretory centre controlling the glycogenic activity of the liver. The removal of the pancreas eliminates this control, and renders an excessive activity of the liver more serious. The fixation of torrents and the planting of the mountains, by M. Chambrelent. It has been calculated that in the last forty years France has suffered losses amounting to 700 million francs due to inundations in places where the mountains were not wooded sufficiently to check the ravages of mountain torrents after heavy rain. The Chamber has recently voted a sum of 2,600,000 frcs. for the planting of the mountains, and it is hoped that the work will be completed in twelve or fifteen years. On the cause of the variations of terrestrial latitude, by M. Hugo Gylden.-On some new derivatives of phenolphtaleïn and fluorescein, by MM. A. Haller and A. Guyot.-On the diameters of Jupiter's satellites, by M. J. J. Landerer.-On a class of dynamical problems, by M. P. Staeckel.-On surfaces whose principal planes are equidistant from a fixed point, by M. Guichard.-On a theorem of M. Stieltjes, by M. Cahen.On a partial differential equation of the second order, by M. J. Weingarten. On the calculation of stability of ships, by M. E. Guyon.-On electric waves in wires, and electric force in the vicinity of a conductor, by M. Birkeland.-Oscillographs; new apparatus for the study of slow electric oscillations, by M. A. Blondel.-Photographic reproduction of gratings and micrometers engraved on glass, by M. Izarn. Ammonium bichromate in gelatine gives better results than either collodion or silver salts in gelatine. Copies of microscopic divided scales and gratings were obtained easily and with certainty, and reflection gratings were produced by employing silvered instead of plane glass.-Concerning the direct-reading stereo-collimator of M. de Place, by M. R. Arnoux.-On the industrial preparation of aluminium, by M. A. Ditte. The alkaline aluminates are decomposed by water, and even in the presence of an excess of alkali the introduction of a few crystals of aluminium hydrate into the solution suffices to prevent the establishment of equili