ASTRONOMY FOR 1889, 1890. 147 



Of the proposed change of the begiuuing of the astro Qomical day from 

 midday to the preceding midnight nothing has been heard since the 

 original agitation of the subject at the time of the Meridian Conference 

 at Washington in 1884^. 



The moon's physical Ubratioti. — Dr. Julius Franz of the Kiinigsberg 

 observatory has done an excellent piece of work in bringing to light 

 and discussing (vol. 38, Konigsberg Beobachtungen) tlie observations 

 of the moon made by Schliiter, an assistant of Bessel's, in 1841-1843, 

 the work having been undertaken by Schliiter under the immediate 

 supervision of his distinguished chief. The observations were continued 

 by Wichmann after Schliiter's death, but Wichmaim was never able to 

 do more than to reduce his own observations for preliminary results to 

 be used in a discussion of all the material available. 



Dr. Franz recommends the substitution of observations of the spot 

 Mosting A for those of the limbs, in determining the moon's place, a 

 method upon which a report was published by the late Dr. C. H. F. 

 Peters in the U. S. Coast Survey volume for 1856. 



Temperature of the moon. — A memoir on the temperature of the moon 

 by Mr. S. P. Langley forms a part of the fourth volume of the publica- 

 tions of the National Academy of Sciences, and is re-published in a some- 

 what abbreviated form in the American Journal of Science for Decem- 

 ber, 1889. The paper may be regarded as the completion of a piece of 

 work commenced in 1883, and represented by papers read in 1884 and 

 1886, as well as the present one. The principal conclusion drawn is 

 "that the mean temperature of the sunlit lunar soil is much lower than 

 has been supposed, and is most probably not greatly above zero centi- 

 grade." The principle by which this temperature is estimated is that 

 the position of the maximum in a curve, representing invisible radiant 

 heat of different wave-lengths, furnishes a criterion as to the tempera- 

 ture of the radiating solid body. In the lunar spectrum two distinct 

 heat maxima are found — one corresponding to radiation reflected from 

 the soil, the other to that emitted by it (when warmed by sunshine). 

 The determination of the second maximum with accuracy would give 

 an accurate value foi: the temperature of the sunlit soil ; but, unfortu- 

 nately, the absorption-bands produced bj^ the earth's atmosphere ob- 

 scure this maximum, and render the conclusions somewhat uncertain ; 

 so that Professor Langley is compelled to state his principal conclu- 

 sion in a guarded manner, as above quoted. 



The Proceedings of the American Academy of Arts and Sciences 

 (vol. 24) contains an account of some measures of lunar radiation made 

 by Mr. C. C. Hutchins, by means of a new thermograph which he has 

 devised. This instrument consists of a single thermal junction of nickel 

 and iron place<l in the focus of a small concave mirror, and is found to 

 be much more sensitive than a thermopile of forty-eight couples. The 

 measures of lunar radiation were made with an arrangement similar to 

 that of a Herschel's telescope with the thermograph in place of an eye 



