pitate, which soon becomes black, and sulphuret and sulphate of silver are produced. The salts of mercury and platina are precipitated black by this acid; and it will be observed that it acts on the different salts in the same way as hyposulphate of potash. Nitric acid reacts instantaneously on concentrated hyposulphurous acid, nitric oxide is evolved, sulphur is deposited and the solution contains sulphuric acid. The action of chloric acid is not less remarkable than that of nitric acid; the decomposition of both acids occurs instantaneously, with tumultuous action; sulphur and chlorine evidently appear, and reagents show the presence of sulphuric acid in the solution: the phænomena are similar to those observed when chloric acid is dropped into alcohol or æther. In this latter case as in those also happens inflammation of the excess of the combustible body. - L'Institut, No. 327. ON THE PRESENCE OF IODINE IN COD OIL. BY R. F. MARCHAND. The different statements of chemists with regard to the presence of iodine in cod oil (Leberthrane) appear to have arisen from the circumstance of those who have not found it having examined impure oil. Cod oil was examined by a chemist of this place which had been received direct from Bergen, without his having succeeded in detecting any iodine in it. As in all probability its energetic action depends upon the presence of iodine, that statement might lead the medical professor to reject Bergen cod oil. I have also received cod oil from the same source which was certainly pure. I examined it according to Gmelin's method (Ann. der Pharm., B. xxxi. p. 523.) which is both a simple and sure method. This indicated the presence of iodine in a manner about which there could not be the least doubt. Twenty grammes was about the quantity acted upon.-Journal für Praktische Chemie. 1840. No. 4. MR. M'CORD'S OBSERVATIONS ON THE SOLAR AND TERRESTRIAL RADIATION MADE AT MONTREAL. A Meteorological Register for 1838 was some time since kindly communicated to us by Dr. Daubeny, kept at Montreal, Lower Canada, in lat. 45° 50′ N., lon. 73° 22′ W., by J. S. M'Cord, Esq., Corresponding Secretary to the Natural History Society, and Member of the Literary and Historical Society, Quebec. It is an abstract of observations of the Barometer, Thermometer, Rain Gauge, Snow Gauge, Actinometer, and Register Thermometer; all made by the first British artists, and carefully compared with standard instru ments. The mean pressure of the year, corrected and reduced to 32° Fahr. is 29.884 in.; the mean temperature, (mean of maxima and minima by Register Thermometers) 41-58. We extract the observations of the solar and terrestrial radiation entire, principally because so few observations have been made pub lic, or even we believe instituted, with the Actinometer, an instrument which we are glad to see appreciated by distant observers. REMARKS. These observations were made during the warmest and brightest days of July, on the Montreal mountain, place of observation 307 feet above St. Lawrence. The first column gives the day and hour; the second, the indication of Sir John Herschel's Actinometer,-by Robinson, London, -mean of three observations; the third, the temperature of air in the shade, Thermometer 5 feet above the earth; the fourth, the indication of the Thermometer placed in the sun on garden mould, not blackened, after an exposure of ten minutes. N.B. This Actinometer was, in Sept. 1837, compared on the same spot, with one in the possession of Dr. Daubeny, of Oxford, England, and gave similar indications, July.. 18 to 19 The first column indicates the 24 hours during which the observation was made, reckoning from 9 A.M. of one day to 9 A.Μ. of the next; the second gives the mar. of the Thermometer in the shade, for the same period; the third, the min.; the fourth, the indications of a register spirit Thermometer, placed on a grass plat and exposed freely to the heavens during the night. All these instruments are made by first artists, British, and carefully compared with standards. Aug.. 6 to 7 76 61 49 SE. do. METEOROLOGICAL OBSERVATIONS FOR MAY, 1840. Chiswick.-May 1. Slight haze: fine. 2-4. Hot and dry with easterly wind. 5. Overcast. 6, 7. Slight haze. 8. Heavy showers: fine. 9. Rain with sultry intervals. 10. Cloudy: sultry. 11. Drizzly. 12. Overcast. 13. Rain: sultry. 14. Cloudy and fine. 15. Heavy rain with thunder. 16. Cloudy: showery: hail shower at 124 г.м. 17. Rain. 18. Cloudy and fine: rain. 19, 20. Cloudy and cold. 21. Clear and cold. 22. Overcast. 23. Clear and fine. 24. Overcast: rain. 25. Cloudy. 26. Rain. 27-30. Very fine. 31. Hot and dry: cloudless. Cloudy. 7, 8. Cloudy: rain 10. Cloudy: rain early A.M. Boston. May 1. Cloudy. 2-4. Fine. 5, 6. early л.м.: rain P.M. 9. Rain rain early A.M. 11. Rain: rain early A.M. 12. Cloudy: rain early л.м. 13. Rain. 14. Cloudy: rain with thunder and lightning P.M. 15. Rain. and P.M. 18, 19. Cloudy. 20. Cloudy: rain P.M. Cloudy. 25. Stormy: rain Α.Μ. 29. Stormy. 30, 31. Fine. 26. Rain rain A.M. 16, 17. Cloudy: rain A.M. 21, 22. Stormy. 23, 24. 27. Cloudy. 28. Fine. 11. Applegarth Manse, Dumfries-shire.-May 1, 2. Beautiful day. 3. The same: Thermometer in shade 75°. 4. Very dry and warm till P.M. 5. Very droughty. 6. The same increased: cloudy. 7. Slight showers all day. 8. The same A.м.: cleared up. 9. Slight showers early л.м. 10. The same: thunder P.M. Rain heavier. 12. Rain nearly all day. 13. Fair. 14. Showery P.M.: thunder. 15. Occasional showers: thunder. 16. Rain preceding night: clear day. 17. Rain in the night: fair. 18. Fresh and cool. 19. Dry and rather boisterous. 20. Dry and more moderate. 21. Very droughty: clear sky. 22. Calm and 23. Showery: high wind. 24. Showery. 25. Showery, and very high 26. Fresh and showery. 27. Fine A.M.: wet P.M. 28. Very wet till P.M. 29, 30. Fine growing day. 31. Variable: bright at midday: wet evening, warm. wind. 1. 2. 1234567 3. 19. 20. 21. 22. 30. 31. Mean. 29-911 29-948 29-867 29-33 5. 6. 7. 30.356 30-343 30-325 29) 30-25 30-23 48-7 10. 11. 12. 23. 29-62629-689 29-883 29-06 29.55 29-89 55.8 26. 28. 29. Dew point. Lond.: 50 52 49 48-7 70 41 58.5 73 49 45.4 66 46 52 62 45 NW. E. E. EbyN. ... ... ... 49 49.0 68 49 50 52 40 0-18 51 49.7 68 50 51 46 42 sw. sw. calm ENE. 011 ... 03 51 ... 54.7 70 51 55 50 41 S. S. calm ENE. ... 54.0 71 51 55 50 424 SE. SE. calm NE. 063 60 56 ... 53 53.3 72 50 51-6 55 50 49 54 39 NW. N. NE. NE. 133 01 15 53 ... 51-2 62 48 51.5 50 40 49.8 67 49 53 56 43 N. S. calm E by s. 180 ... 05 0-71 52 51.9 66 50 55 63 44 s. S. 53-2 60 49 53.5 64 48 NW. sw. calm NW. 450 41 31 ... 55 51.4 65 47 56 58 48 s var. sw. w. NW. 447 50-2 62 46 55 53 45 S. S. calm NNE. 033 09 14 52 48.3 62 45 49 531 42 w. w. NE. NW. 250 0115 51 THE LONDON AND EDINBURGH PHILOSOPHICAL MAGAZINE AND JOURNAL OF SCIENCE. [THIRD SERIES.] AUGUST 1840. XIII. On the Theory of the dark Bands formed in the Spectrum from partial Interception by transparent Plates. By the Rev. BADEN POWELL, M.A., F.R.S., F.G.S., F.R.Ast.S., Savilian Professor of Geometry in the University of Oxford*. (1.) THE phænomenon of peculiar dark bands crossing the prismatic spectrum, when half the pupil of the eye (looking through the prism) is covered by a thin plate of any transparent substance, the edge being turned from the violet towards the red end of the spectrum, was first described by Mr. Fox Talbot in 1837 (Lond. and Edinb. Phil. Mag. and Journal of Science, vol. x. p. 364.), who showed that these bands are due to the interference of the two halves of each primary pencil, one of which is retarded by the plate. (2.) Sir David Brewster has given various new modifications of these experiments (British Association Reports, vol. vii. Trans. of Sections, p. 13.), the most material of which tend to show that the effect is fully produced only when the plate is in the position just described, and diminishes and disappears as it revolves in its own plane; the same observation being also extended to the case of the spectra formed by interference from grooved surfaces, or gratings. (3.) The explanation given by Mr. F. Talbot accounts for the production of the bands simply, but assigns no reason why the interception must take place on one side more than the other. That it does so, is considered by Sir David Brewster as indicating an entirely new property of light; having reference to the different sides of the pencil related to their position of greater or less refrangibility, and which he has not inexpressively termed a peculiar " polarity." • Communicated by the Author. Phil. Mag. S. 3. Vol. 17. No. 108. Aug. 1840. G (4.) My attention was drawn to the subject in the course of last summer, when I repeated the experiments, and devised several new modifications with reference to an explanation which it appeared to me was supplied by the undulatory theory; to these investigations I referred briefly at the Birmingham meeting of the British Association, 1839. For several reasons (on which I need not here enter) I have delayed publishing any details; nor should I do so now, but that having learned that Mr. Airy has recently pursued the research to many entirely new conclusions*, I am anxious to put on record the few points I have been able to establish, and to vindicate my views from misconceptions to which they have been exposed. (5.) The following distinctions are important to be borne in mind with reference to the explanation of the phænomena. In these experiments we have to consider the different elementary pencils of which the spectrum, as presented to the eye, is formed; and with respect to each of these, in the case of the prismatic spectrum it is easily seen that the edge of the plate intercepts that half which lies towards the EDGE of the prism. In the interference-spectrum (according to Fraunhofer's method), the spectra are formed one on each side of the axis, with their violet ends towards it. The edge of the plate in this case must always intercept that half of each primary pencil, which after passing the focus lies NEAREST to the axis. (6.) I have found that with the same prism the intercepting plate must be within limits of thickness, which differ according to the substance of the plate, and with the same plate the character of the bands differs with the medium of which the prism is formed. These differences appear to depend on the refractive and dispersive powers powers of the substances. (7.) With a prism of flint glass and a plate of mica, the greatest thickness which can be used may be about the Tooth of an inch. In this case the bands appear fine and numerous, and it seems only in consequence of their increase in number that they cease to be distinguishable when the thickness is increased beyond this. If we use less thicknesses (such as those into which mica is easily split) the bands become broader and fewer, and at length faint and ill-defined. It is perhaps not possible to distinguish them if fewer than four or five are formed throughout the spectrum. The bands are never very dark; showing that only a portion of the rays is concerned in their formation. [* A notice of Mr. Airy's paper on this subject will be found in our report of the proceedings of the Royal Society for June 18, 1840.-EDIT.] |