300 POPULAR LECTURES AND ADDRESSES. 



kettle, and then toasted before a hot fire, without 

 in any sensible degree warping the aluminium 

 rim or disturbing the degree or point divisions 

 printed on the paper ; and in its proper place 

 under glass in its bowl it remains quite undis- 

 turbed through all variations of temperature 

 from coldest weather to hottest sun in actual 

 sea-service. 



The entire weight of the card is about 170 

 grains, made up as follows : 



Aluminium rim ......... 76 grains. 



Eight needles ....... . . 54 ,, 



Aluminium nave ........ 2 ,, 



Aluminium and sapphire cap ... 2| ,, 



Paper ............. 28 



Silk thread ..... .... 8 , 



Total 



This is a seventeenth of the weight of the ordinary 

 ten-inch compass hitherto in common use in the 

 best-found merchant steamers, which is about 

 six ounces. On the other hand, the vibrational 

 period of the new ten-inch compass, which at 

 Glasgow is about forty-two seconds, is nearly 

 double that of the ordinary ten-inch compass. The 



