VELOCITY OE WHITE AND OF COLOURED LIGHT. 
269 
The following is a summary of these results 
12th and 13th equalities. 
9 9 
99 
99 
99 
1881 January 20, Nos. 3 
99 
99 
13th and 14th equalities. 
99 
99 
9 9 
General mean of both sets . 
1 and 2 
Y= 187,707 miles per second. 
5 „ 6 
188,405 
9 9 
8 „ 9 
187,676 
99 
9 „ 10 
186,457 
99 
LO „ 11 
185,788 
99 
3 „ 4 
186,495 
99 
5 „ 6 
187,003 
99 
equalities: 
Y=187,076 
99 
2 and 3 
Y= 186,1.90 miles 
per second. 
6 „ 7 
186,830 
9 9 
7 „ 8 
187,266 
>> 
2 „ 3 
188,110 
99 
3 „ 4 
188,079 
99 
qualities: 
Y=187,295 
Y=187,167 
99 
Multiplying this by the mean refractive index of air ( = 1 ‘0002 9) we obtain the value 
for the velocity in vacuo, viz.: 187,221 miles per second. 
This must be corrected for the rate of our clock. 
One second of our clock is equal to 0T99723 of a mean solar second. 
Dividing the value found for Y by this quantity, we obtain the final value for the 
velocity of the white light from an electric lamp in vacuo, viz. :— 
Y—187,273 miles per second (log=5*2724757) 
= 301,382 kiloms. per second (log=5’4791167) 
Using Struve's constant of aberration 20 // ‘445. 
The resulting parallax of the sun is =8"'77. 
Distance of the sun =93,223,000 miles. 
The value obtained by Cornu,* using the method of Fizeau, was 300,400 kiloms. 
per second. He nearly always used the Drummond (or lime) light. A few experi¬ 
ments were made with a petroleum lamp. 
* “ Ann ales cle TObservatoire de Paris ” (Memoires, tome xiii.), 1876 
