TRANSACTIONS OF SECTION A. 



625 



[I' 1)6 the 

 L'lnissivity 

 IVereuce of 

 time ; atul 

 :lie tempe- 



:>nt. flowiiijr 

 uteil l)v the 



[ tlui tempe- 

 •esistanci' nf 

 ;, ftiid liciue 

 i])eniture nt' 

 le sui'facu in 



uto measure 

 icatt'd to the 

 itod in Plot', 

 oxpovimeiits 

 ipeiuU'd in ft 

 lueter and 00 

 V. Macfarlane 

 ri' centimetre 

 ng Ixiily and 

 a little more 

 excess of >)' t ' 



and with tlie 



n of a wire 



_.;i.-. 1 have 



- 1 - down til 



•JllOO 



nil excess ni 

 1 have wade 

 ;; eniissivity. 

 •lion and eon- 

 )y small wire^ 

 .•-pump. Tbis 

 .it.and witliia 

 ;lly, and unich 

 thouffli in ni> 

 (i. The coii- 

 iftt there is a 

 ise being very 

 V atmospheric 

 eteuesa. H" 

 aven with the 

 Trying oil" heat 



bright snrface 

 aas tuljc about 



Taiile I. (Quoted from a Taper to the Royal Society.) 



* The temperature prol)at)ly much too low. Tlie wire .xajri^ed down with heat, 

 and touched t lie sides of th(! tube at several points. Tlic result calculated for eniis- 

 sivity from 140=" is (' = 5^'--. 



The folldwing table may also be found interesting. It shows the emis.sivity in 

 absolute measure of several materials commcmly used as insulating coverings' for 

 wires in air of ordinary atmospheric pressure. 



Taiu.!': II. (Quoted from a Taper to the Tioyal Society.) 



Spccifyinj:; Xumlicr (H.W.G.) 

 and nature of covering 



No. 22 Silk covered . . 



No. 20 Cotton covered . 



No. 2(5 Silk covered . . 



No. 22 (iutta-perclia . . 



No. 22 Tinned, Gutta-jier-' 

 eha-ei)veredand l->oublo 

 Cotton-covered outside 



Z i> z ii 



•"fi 



•50 

 •45 

 •72 



•73 



Eniissivity 



O'OO 13.33 

 0^001 385 

 0002020 

 000085.1 



0000759 



I). On a Gi/rostati'e Worl-litii "Mmlrl of tlw Magnetic Compass. 

 JUj Professor Sir Wii-'iJAM Thomson, LL.D., F.B.S. 



In my communication to the Britisli Association at Southport,' I explained 

 several methods for overcoming the dilliculties which had rendered nugatory, I 

 believe, all previous attempts to realise Foucault's beautiful idea of discovering with 

 perfect detiniteness the eartii's rotational motion by means of the gyroscope. One 

 of these, which I bad actually myself jiut in practice with partially satisfactory 

 results, was a 



Gtkostatic Balance for Measuring the Vertical Component of the 



Earth's Kotation. 



It consisted of one of my gyrost ats supported on knife edges attached to its contain- 

 ing ca.se, with their line perpendicular to the axis of the interior flywheel and above 

 the centre of gravity of the flywheel and framework by an exceedingly small height, 



No report of tliis communication has, so far as I know, hitherto appeared in 



print. 



88 



