470 Prof. Tyndall on Lunar Radiation. 



their phenomena, which are various kinds of motion : of these 

 the principal motions seem to be radiations by undulations, and 

 circuits by polarization. When the former relate to material 

 molecules, the phenomena are best known as sound ; when they 

 relate to the medium sether, they become luminous arid calorific 

 phenomena : and so likewise the polar actions of molecules are 

 known as electrical and magnetic phenomena ; those of sether, 

 as the tangential curi'ents due to gravitating and centrifugal 

 forces. And should the same ratio of velocity as occurs between 

 sound and light hold good between electricity and centrifugal 

 force, and between magnetism and gravitation, the cosmical forces 

 gravity and centrifugy must evidently be instantaneous in their 

 operations, and not successive by undulations like radiant heat 

 and actinism. 



Claverhouse, near Dundee, 

 October 1861. 



LIX. Observations on Lunar Radiation. 

 By Professor Tyndall, RR.S.* 



I HAD hoped, before the appearance of the present Number of 

 this Magazine, to be able to prosecute the observations on 

 Lunar Radiation referred to in my letter to Sir John Herschel 

 to a definite issue ; but I am so closely occupied with inquiries 

 of another kind, that I must for the present content myself with 

 recording the observations on which the remarks contained in 

 the letter referred to were founded. 



My place of observation was the roof of the Royal Institution 

 in Albemarle Street, where I had a platform erected, sufficiently 

 high to enable me to sweep a large portion of the heavens with 

 my thermo-electric pile, without impediment from the chimney- 

 pots. Wires were carried from the pile to an excellent galvano- 

 meter placed in the laboratory, the floor of which was about 

 seventy-two feet below the platform. 



On directing the axis of the pile towards the heavens, the 

 chilling produced by radiation from its exposed face was so 

 considerable f, and the consequent galvanometric deflection so 

 great, that it was quite hopeless to operate on the needle in this 

 position. To move it a single degree would have required 

 many hundred times the quantity of heat or cold necessary to 

 urge it through one of the lower degrees of the galvanometric 

 scale ; I therefore operated as follows : — 



* Communicated by the Author. 



t I intend to make this mixed action of our atmosphere aud stellar 

 space the subject of a special investigation. At midday also the refrige- 

 ration, of the zenith is. very great. . . 



