NUMBERS AND MEASURES. 



(119) ELASTIC CONSTANTS OF QUARTZ FIBRES. 



A fibre *01 cm. in diameter will allow of a twist of 1 turn for 

 each 3 cm. of length and carry from 600 to 860 grams. : 



Simple rigidity, n = 2'8815 X 10" C.G.S. 

 Young's modulus, ft = 5 '1785 X 10" C.G.S. 

 Bulk modulus, K - 1'435 x 10" C.G.S. 

 Coefficient of linear expansion, '0000017. 

 Refractive index for sodium light, 1'4587. 

 Temperature coefficient for n t "00013. 



(79) ROUGH DATA IN ELECTRICITY. 



Amperes of current in a telegraph on land '003 



,, ,, an incandescent lamp *5 1 



,, ,, an arc lamp 5 400 



Difference in volts giving 30 cm. spark in air 90000 



,, ,, dangerous to life 1000 



,, in incandescent lamp 50 -100 



Candles per horse-power in incandescent lamp 100 230 



arc lamp 4001000 



Watts required by 1 6-candle lamp (Munich) 60 80 



,, ,, 20-candle lamp (Perry) 75 



Efficiency of transformers '955 '97 



Mechanical efficiency of Munich railway 



