182 SCIENTIFIC RECORD FOR 1884. 



inequality, so ShS to start together from the same absolute time, it is 

 found that the solar maximum occurs about eight or nine days after one 

 of the Toronto maxima, and the Kew temperature-range maximum 

 about seven days after the same Toronto maximum. 



4. The proportional oscillation exhibited by the temperature-range 

 inequalities is much less than the proportional oscillation exhibited by 

 the corresponding solar inequalities. {Nature.) 



Variations in the Sun'' s diameter. — A pamphlet of 17 pages by Dr. 

 Hilficker, of the Observatory of Neuchatel, treats the 3,408 observations 

 of the Sun made by eight observers during the years 1802-83, with the 

 object of determining whether the Sun's diameter varies. The meridian 

 circle has an aperture of IIS™'", and a magnifying power of 200 is used, 

 and each limb of the Sun is observed on 13 threads, so that these obser- 

 vations are more suitable for the i^urpose than many other series which 

 have been used for the purpose. Besides the Neuchatel series, others 

 are quoted, though several papers on the subject are not referred to. 



Dr. Hilficker gives two conclusions, which he regards as satisfactorily 

 proved by his discussion. These are (1) that the variations in the 

 diameter of the Sun shown by the I^^'euchatel observations are real; 

 (2) that these changes depend upon the period of the solar spots ; that 

 is, that the largest diameters co exist with the minimum Sun-spots, and 

 vice versa. 



It will be noticed that this conclusion does not agree Avith those of 

 other discussions, notably with the very satisfactory one of Dr. Auwers, 

 based on the results of the observations of seven observatories, or with 

 the discussion of corresponding observations at Greenwich and Wash- 

 ington, by Professors Newcomb and Holden. 



The Moon. — Dr. Th. von Oppolzer, of Vienna, has lately published an 

 attempt to explain the discrepancy between the observed value of the 

 secular acceleration of the moon's mean motion and that derived from 

 the mathematical theorj' by Delaunay and Adams. This difterence has 

 heretofore been supposed to be accounted for by the continued retard- 

 ing action of the tides on the rotational velocity of the earth ; but Pro- 

 fessor Oppolzer, accepting the now generally believed pervasion of in- 

 terplanetary space by comminuted cosmical matter, proceeds to esti- 

 mate the threefold action of such matter on the motions of moon and 

 earth. First, the masses of both bodies are continually receiving slight 

 increments from the accumulation of this dust upon their surfaces. Sec- 

 ond, a part of this increment of the moon's mass acts in such a way as 

 to decrease its tangential volocity. Third, the continued deposition of 

 cosmical dust on the surface of the earth changes its rotational velocity, 

 afiecting thus the apparent motion of the moon. All these eliects are 

 reduced to numbers, in the form of co-efficients of terms in the moon'^ 

 mean longitude multiplied by the square of the time, and by an un- 

 known quantity which represents the thickness of a layer of cosmical 

 dust which falls on the surface of the earth in a century. If this latter 



