TRANSACTIONS OF SECTION A. 



625 



Table I. (Quoted from a Paper to the Royal Society.) 



* The temperature probably much too low. The wire sagged down with heat, 

 and touched the sides of the tube at several points. The result calculated for emis- 

 sivity from 140° is £ = 57^. 



The following table may also be found interesting. It shows the emissivity in 

 absolute measure of several materials commonly used as insulating coverings for 

 wires in air of ordinary atmospheric pressure. 



•6. On a Gyrostatic Working Model of the Magnetic Compost 

 By Professor Sir William Thomson, LL.D., F.R.S. 



In my communication to the British Association at Southport, 1 I explained 

 several methods for overcoming the difficulties which had rendered nugatory I 

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

 perfect definiteness the earth's rotational motion by means of the gyroscope. One 

 of these, which I had actually myself put in practice with partially satisfactory 

 results, was a J 



Gyrostatic Balance for Measuring the Vertical Component op the 



Earth's Rotation. 



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

 ing case, 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 this communication has, so far as I know, hitherto appeared in 

 print. rr 



1884. ss 



