f 



65A 



REPOUT — 1884. 



^i,l^' 





. i*!" 



10. On, tlio Vehcifi/ of Ttiijhl in Oarhnn "Dhnlpliilfi ami Ihr Vi'Jj'n'rnpi', in 

 Vflorlty of Red ami Jlliu' Liijhf in thr mnnf. Hij Al.liEiiT A. A[l('lii;r,soN. 



TIit> Rn'anf,'(!ni<'nf of apparatus was ('.ssciitiallv tlu' smut! as in tlic expt'i-iinonts cif 

 Foiicaiilt. Tlu) liquid \viis coutainoil in a tulu' 2 reel lonj,', willi plalt'->j:laHs end.-*. 

 With about .'!()0 turns per socond, and a radius of liO fctsl, a delloction of \\ mm. 

 was obtained. 



Thu principal difliculty was tin' ubtainiiiy' a clear iniii^^i' lln'ouf^b the li(|uiil. 



Tiio ratio of tlio volocily in tli'' li'|uid to that in air was found to hn as oni) to 

 r75. Till! thi'ort'tical value is the refractivo inilex of the li(iuid, or 1 •(!"), 



In the second ])a\'i of tho work the liirht was coloured by a liireet-vi^ion prisni 

 planed lieforo the slit. The colours selected were halfway hetweeii 6' and /> and 

 halfway biitween b and /'. 



It was found lliat the rod ray travelled 21 per cent, faster than tlio blue, wliich 

 is in accord with theory. 



11. On a iSystemalic lieacari'Ji fur Sfartt villi, a Mcnmirahlo AnnnnJ VnrnUax, 



and its Restdls. Bij Profc ssor Roiieht S. 13.uj,, LL.D., F.R.8. 



12. On (in Eh'i-trnchjnaiiinwcfer, villi fxln'mrhj liijlif, mocin'i coil, fnr Ih 

 metisnrcmoul of snuill allei-nalimi cnrrentx.^ Hij Dr. W. H. Stonk. 



The niovinj; coil is made of aluminium wire, which for i^nven mass conducts 

 better than any known substance. This is silk-covered, and wound in an anchor- 

 rinfr-sha]ied form on a hollow bobbin of cork. The two ends ani brouf^ht up to a 

 small ]ihito of e')onite, and connecticm is perfectly made by means of minute 

 damping' scniws, with a bilihir suspension of |j:ilt silver wire. The ))obbiu is tlien 

 immersed in ii -mail tank of petroleum oil, whicli serves at once (1 ) to lessen its 

 wei;.dit, ('2) to act as a preserver of the insulation, and (.'») to damp any excessive 

 vibration. 



Tlio instrument has tlie crreat additional advantapre of moving: ([uickly up to its 

 full deflection, and thus ^'ivini,' less time for the runniui,' down of tho battery 

 attached to the primary induciiifi' coil than that which occurs in the ordinary form 

 of the instrument. As cork swims in heavy petroleum him]) oil, and the silk- 

 covered alnmuiium wire sinks, a C(mibination of tlio two of any j,nveu specilie 

 gravity within certain limits can easily be obtained. (See ' Nature,' Oct. .'{(), 1884.) 



13. On llic //(((« ri'ijidatinij llie Connection hetirccn Currcnf and IntcnsHij 

 of Incandescence of Carbon Filaments in (llmv Tramps. Ji// W. H. 



PUEECK, F.R.S. 



In a pa])er read b(!fore tho IJoyal Society in 1SS■'^ I ])iiinted out, from experi- 

 menfid data, that the light emitted by a jrlow lamp varied ii]iparonlly as the sixth 

 power of the current. 



I have veritled this law, not only by subsequent ex]>eiimenls of ray own, bat, 

 which is much more satisfactory, by experiments of others. Professor Kittler, of 

 Darmstadt, and Captain Abney have made, independently of each other, most 

 careful and exhaustive measureme'Uts in this direction. I have tabulated and 

 traced them out in curves, which I submit. They fully confirm the law that 



L = kO' 



but within limits, and that tbese limits embrace the ordinary rauf^e of a^^low lamp 

 wlien used for artificial illumination. As long as the resistance and tbe current. 

 vary uniformly together, the, law holds good ; but as the state of incandescence is 

 increased, a ])oint is readied, varying with each kind of lamp, when the r(!sistance 

 ceases to dinnnish at tbe same rate, and eventually to increase. When this occurs 

 tbe law is departed from, and the light emitted increases much faster than the 



• See Is^ature, October 30, 1881. 



