404 SCIENTIFIC RECORD FOR J 883. 



of lunar than of solar heat, drew (as is well known) the inference that 

 the lunar surface in sunshine was nearly of the temperature of boiling 

 water. We find no evidence whatever of this, but are led by other ex- 

 periments to believe that the fact (which we do not question) that most 

 kinds of glass absorb more lunar than solar heat has no such explana- 

 tion as Lord Eosse assigned to it, but is due to selective absorption of 

 the solar rays by the lunar surface. We find no evidence of any but 

 reflected heat there, and so far as our experiments go, no indication that 

 the absolute temperature of the lunar surface, under full sunshine, is 

 high enough to give any indication whatever of its existence to the 

 most sensitive apparatus we have." 



Virtual change of the astronomical unit of time. — Mr. E. J. Stone has 

 recently communicated to the Eoyal Society a paper on a virtual change 

 of the astronomical unit of time, which has taken place in consequence 

 of the difference between Bessel's expression for the moon's mean longi- 

 tude and the corresponding formulae of Hansen and Leverrier. The 

 investigation was primarily undertaken for the purpose of finding an 

 explanation of the rapidly increasing discordance between the moon's 

 place and that indicated by Hansen's lunar tables; and, after a careful 

 examination of a number of other hypotheses, Mr. Stone thinks he has 

 found the cause as indicated above. 



Up to 1863, Hansen's lunar tables were satisfactory ; since then the 

 error of the moon's longitude has increased from +0".121 to +10 // .265. 



Mr. Stone thinks this will also clear up some perplexing discrepancies 

 in results as to the moon's secular acceleration. He points out that 

 Hansen's tables " cannot safely be used in the discussion of ancient 

 eclipses until the effects of this confusion of units of time have been 

 cleared." 



This paper has been replied to by various astronomers, notably Pro- 

 fessors Adams and Cayley, who have shown that Mr. Stone is here in 

 error. 



MINOR PLANETS. 



The part of the Berliner Aatronomisches Jahrbuch for 1885 containing 

 ephemerides of the minor planets for 1883 has been issued to the various 

 observatories in advance of the publication of the annual volume. It 

 contains approximate places for every twentieth day of 224 of these 

 bodies, the latest being No. 225, with accurately calculated opposition 

 ephemerides of 43, each extending over about five weeks. This division 

 of the Jahrbuch occupies upwards of one hundred pages. 



There are six cases during the year where the planets, approach the 

 earth about opposition, within her mean distance from the sun. On 

 June 22 Phocea is at a distance of 0.93, declination +16°; on July 12 

 the distance of Clio is 0.96, declination — 35£°; on August 1 that of Isis 

 is 0.90, declination — 28°; on October 1 that of Polyhymnia is 0.98, de- 

 clination +8£; on October 20 that of Virginia is 0.98, declination +13°, 



