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♦ KNOWLEDGE ♦ 



[April 17, 1885. 



" The thermometer being taken out of the cylindrical tube, 

 about two-thirds of the substance which is to be the subject 

 of the e.xperiment are introduced into the globe ; after 

 which the bulb of the thermometer is introduced a few 

 inches into the cylinder ; and, after it, the remainder of the 

 substance, being placed round about the tube of the ther- 

 mometer; and lastly, the thermometer beiug introduced 

 farther into the tube, and being brought into its proper 

 place, that part of the substance which, being introduced 

 last, remains in the cylindrical tube above the bulb of the 

 thermometer, is pushed down into the globe, and placed 

 equally round the bulb of the thermometer by means of a 

 brass wiie, which is passed through holes made for that 

 purpose in the stopple closiug the end of the cylindrical 

 tube." 



The temperature he selected as the starting-point was 

 70 Reaumurz^ilOO" Fahr. He preferred this to the boil- 

 ing-point, as he could obtain it accurately by first plunging 

 the whole apparatus duly charged into nearly boiling water, 

 then allowing it to fall to 70°, and immediately plunging it 

 into a mixture of pounded ice and water, where, by the aid 

 of a little agitation, it remained steadily at the freezing- 

 point. 



The matei'ials he first examined were raw silk, as spun 

 by the worm ; sheeps' wool, cotton wool, linen in the form 

 of the finest Unt, being scrapings of very fine Irish linen, 

 the finest part of the fur of the beaver, separated from the 

 skin and from the long hair, the finest part of the fur of a 

 white Russian hare, and eider-down. Sixteen grains of 

 each of these were used by placing them in the globe of the 

 passage thermometer in the manner above described, 

 arranging them equally around the mercurial bulb. 



As the interstices of these bodies were filled with air, his 

 first experiments were made with air alone, with the fol- 

 lowing results : — 



The figures in the second and third column tell the 

 number of seconds occupied in losing the successive amounts 

 of heats between 70° and 10° Reaumur. The third experi- 

 ment shows the time required for gaining the temperatures 

 stated in the fourth column, when the passage thermometer 

 was immersed in boDing water at the moment it registered 

 10 . (The Reaumur freezing-point is 0.) 



The following table shows the results with the various 

 substances therein mentioned, the quantity in each case 

 (excepting the first, which is a repetition of the first of the 

 above-named experiments) being 16 grains. 



The clothing value or " warmth " of these substances as 

 thus applied varies directly with these figures representing 

 their power of resisting the passage of heat, or their " non- 

 conducting power." 



He says : " I acknowledge that the difTerences of warmth 

 of these substances were much less than I expected to have 

 found them," and adds that this might arise from theu- 

 volumes or solid contents being diflerent, though their 

 weights were the same. He therefore made further experi- 

 ments, which I will describe in my next. 



IS THE DIAMETER OF THE PUPIL OF 

 THE EYE AN EQUIVALENT OF 

 THE LIGHT'S INTENSITY? 



By John Gorham, M.R.C.S. Eng. 



(From a paper read before the Eoj-al Society in November, 1884.) 

 (_Contmued from page SOO.) 



TO obtain additional and still more conclusive evidence 

 of the correspondence between the pupil's size and 

 the light's intensity, experiments were now made on a 

 larger scale, the pupil of the eye being measured every 

 consecutive hour, from 9 a.m. to 7 or 8 p.m., daily, for a 

 period of three months. From these experiments it was 

 clearly and satisfactorily developed, that certain definite 

 magnitudes of the pupil repeated themselves at definite 

 periods or intervals, either of hours, days, or months, and 

 that these magnitudes coincided with the kind of light by 

 which they had been stimulated into existence. 



Mean diam. of the pnpil in hundredths of an inch 



From this Table, which embodies the results of one thou- 

 sand experiments, it appears that during the three con- 

 secutive months of April, May, and June, 1884, the 

 pupil's magnitude became gradually smaller and smaller, 

 thus keeping pace with the gradual increase in the light's 

 intensity. Again, that if we take the mean of all the 

 diameters for each hour, and set them in parallel columns, 

 we find that on any given hour the pupil is more dilated 

 in April than in May, and in May than in June, thus coin- 

 ciding with the light's increasing brilliancy at these suc- 

 cessive periods. 



Again, it was reasonable to anticipate that the mean 

 light would be stronger, and, if so, that the mean size of 

 the pupil would be smaller on each succeeding month. It 

 was found accordingly that the mean size of the pupil in 

 April was = -119 in.— in May '094, and in June -086 in. 



Abundant evidence has been adduced to show that the 

 pupil's movements and the light's intensities are mutually 

 reciprocal. In no single instance has the pupil been found 

 to make, so to speak, a false move. It has never contracted 

 when stimulated by a weak light, or dilated by a strong 



