524) . Prof. Lovering on the Velocity of Light 



Heat. 



Chemical. Voltaic. 



A. Zinc, sulphate of zinc ...Copper, sulphate of copper... 23564 23602 



B. Zinc, acetate of zinc ...Lead, acetate of lead 15691 12438 



C. Copper, nitrate of copper... Silver, nitrate of silver 16402 7789 



Thus, while in the element A the current reproduces the che- 

 mical heat in its entirety, the current in the element C does not 

 reproduce more than half. What is the reason of this different 

 action in two cases so similar? This is a serious difficulty, 

 worthy of the attention of physicists. 



LXXV. On the Velocity of Light and the Sun's Distance. 

 By Prof. Joseph Lovering, of Harvard College*. 



FOUCAULT'S recent experiment on the velocity of light, 

 though of a less popular character than his celebrated 

 pendulum experiment to prove the earth's rotation, will never- 

 theless attract even more attention among men of science. If its 

 results are placed beyond doubt, they will affect astronomy to a 

 degree not possible for the pendulum experiment, unless it had 

 come as early as the time of Galileo. I shall examine Foucault's 

 investigation on the velocity of light, (1) as it influences the 

 science of optics, and (2) as it tells upon one at least of the 

 vexed questions in astronomy. 



In the circle of the sciences, the centre may be placed any- 

 where, and the circumference will be everywhere ; such is the 

 mutual dependence of each upon all the rest. After the science 

 of optics has furnished astronomy with the telescope, the astro- 

 nomer discovers with it the satellites of Jupiter and the aberra- 

 tion of light, and with the help of these phenomena assigns the 

 value of the velocity of light, and thus repays to optics the 

 debt incurred by his own special science. Now, for the first 

 tirne^ the science of optics has relinquished the guardianship 

 of astronomy, ascertained by direct experiment one of its own 

 fundamental data, and thereby possibly put astronomy under 

 a new obligation, to be cancelled, doubtless, with interest here- 

 after. 



Let us glance first at the two astronomical methods of mea- 

 suring the velocity of light. While the senses of touch and taste 

 act only by contact, those of hearing and seeing bring the mind 

 into communication with distant objects. The air and the omni- 

 present aether supply the delicate and ever ramifying threads by 

 which telegraphic intercourse is maintained with the ear and the 

 eye. When the origin of the sound or the light is at a large 

 distance compared with the velocity of the acoustic or luminous 

 * From Silliman's American Journal for September 1863. 



