ON THK TR.MrKKATrRK OK THE SIRFACE OF THE MOON. 



tKoll Kl-:)lt:AR(HE.S MADE AT THE AI.I.EtiHEAy <iHt<EKrATOItr HY K I: I.ANdl.EY. A.S.SJSTEI' BY F. W. VERY A.\D 



.1. E. HEELER. 



l!ni/l llrltthri- 17. 1-'>I4. 



FioiH tlio earliest ages it lias been observed that tlie moon's rajs bring ns b'gbt, bnt no sensi- 

 ble Ileal. When, in the eonrse of time, the ]>henoniena of nature bej;an to be snbjeeted to more 

 exact scrutiny, it was seen that in view of the very obvious briglitness of the moon, the absence of 

 heat in its rays was an anomalous circumstance, and in the last century Tschiiidiausen, La Hire, 

 and others, with the largest burning lenses or mirrors, and the most delicate thermometers of that 

 rime, attempted to obtain indications of heat, but without success. As apparatus improved in 

 delicacy, it began to be noticed that (on the contrary) indications of actual cold were often obtained 

 when the tliermonieter lay in the focus of burning minors whidi concentrated the rays of the moon 

 on it; its concentrated heat, if any existed, being so nearly «//, as to be overbalanced by the in- 

 creased radiation of the thermometer toward space or to the substance of the mirror itself. Other 

 observers, like Howard,* fancied they obtained signs of heat with sensitive thermonieters, but these 

 were doubtless due to inexperience of the precautions necessary in eliminating the ettect due to the 

 radiations from the apparatus itself, radiatio7is which may give delusive indications of marked 

 lunar heat or cold, according (for instance) as the screen withdrawn be itself (colder or warmer 

 than the thermometer by some immeasurably small fraction of a degree. We can hardly overstate 

 the i)robability of error in such a reseaich in any hands but those educated to multiplied precau- 

 tions, such as were used by Professor Forbes, t who, employing a 'ens by which the lunar heat was 

 concentrated about (i,000 times, still obtained no certain e\idence of heat. He was able, however, 

 to conclude from this negative result that the warming efiect of the full moon on the surface of 

 the earth would at any rate not exceed sooVon o^'* «lt>gi'pe Centigrade. 



The lirst satisfactory evidence of actual heat was obtained by .MelIoni,| who, with a polyzonal 

 burning lens of one meter aperture and on^^ meter focus, with the newly invented thermopile, in the 

 clear air of Vesuvius, after due inecautions against instrumental error, was enabled to announce 

 that indications of beat had been obtained, though the eflect was still all but immeasurably small. 

 Prof. tMazzi vSinyth, ? uixm the Peak of Teneritfe. obtained also some apparent indi(!ations of heat, 

 but all these measures, and a large number of others which 1 do I'ot cite, including those of such 

 skilled observers as Tyndall II and Huggins,1] lead only to the conclusion that the moon's heat is so 

 small that we can do little more than detect its existence, though M. Marie Davy** a little later 

 obtains some apparent evidences of the change of heat with phase, indicating a direct eft'ect of 

 about yjToVo-o degree for the full moon, wiiich he observes is about the one-fiftieth part of that found 

 by Smyth. Such was the state of our ex|)erimental knowledge of the subject until the time of the 

 observations of the present Karl of lJi>sse, which, as marking (piite a new order of accuracy in lunar 

 heat measurements, we reserve for a subse(iuent and more detailed discussion. 



' Ameiirun .loiinial (il' Scii'iice, II. |i. :!-29 (18-211). 



t London Pliil. Magazine, vi, ji. IXS (1*!5). 



; Coniptfs icndns, xxii, p. :AI (184()). 



* Report of the Tencritie As(roDoniic:il Kxpei imeiit, aildiessed lo tlie l.ciiils Ciiiiiniissionerx of llie Ailniiiall y. 



II Phil. Mag., IV Series, xxii (1861). 



T Proe. Royal Society, vol. xvii (18(19). 



•'Coniptes rendiis, Ixix (l."'*)!)). 



