382 Chronicles of Science. [July, 



orbit being determined from a careful examination of a long series 

 of observations, the ratio of the sun's distance to the moon's is 

 determined by a simple calculation. Owing to a mistake in the 

 numerical work, Leverrier took the moon's mass at rrVrth instead 

 of sr^th of the earth's. The effect of the correction is to reduce 

 the solar parallax from 8"*95 to 8"*91, corresponding to an increase 

 of upwards of 400,000 miles in the sun's estimated distance. The 

 weak point of the method clearly lies in the great variation result- 

 ing from a very small change in the estimated value of the moon's 

 mass. On this account the observations made use of are better 

 fitted for the solution of the inverse problem, the determination of 

 the moon's mass from the earth's parallactic inequality ; and, in- 

 deed, Delambre has already made use of this method for the pur- 

 pose named. 



The corrected estimate of the sun's distance, by Leverrier 's 

 mode, agrees with Hansen's determination from the moon's paral- 

 lactic inequality. Mr. Stone, who had obtained the value 8"'94 

 for the solar parallax from observations of Mars, has lately deduced 

 the value 8"*85 (with a possible error of 0"*056) from the Green- 

 wich lunar observations made near the epoch of maximum lunar 

 parallactic inequality. It is to be noticed that when Mr. Stone 

 speaks of the last-named inequality as corresponding to the earth's 

 parallactic inequality, he must be understood as speaking merely of 

 nominal correspondence, the two inequalities being quite distinct in 

 character. 



During the late opposition of Mars, Mr. Huggins made several 

 observations of the planet's spectrum. As in former observations, 

 groups of lines were seen in the blue and indigo, but it was not 

 found possible to measure these so as to determine whether they 

 are solar or due to the planet's atmosphere. Again, also, many 

 marked lines were seen in the red. On February 14, faint lines 

 were seen near D, and were judged by Mr. Huggins to be due to 

 absorption by the planet's atmosphere, as, although similar to lines 

 seen in the solar spectrum when the sun is low, Mars was not low 

 enough for the production of the lines, which were not seen in the 

 moon's spectrum though she was lower than Mars. The spectrum 

 of the darker portions of the disc was less brilliant than that from 

 the lighter part, indicating equality of absorption, and that the 

 colour of the darker parts is nearly, if not quite, neutral. 



Mr. Huggins concludes that the ruddy colour of Mars is not 

 due to its atmosphere, but to the materials of the planet's body; 

 and he remarks that the polar regions show no colour, though the 

 light from them traverses a greater depth of atmosphere than that 

 from the central parts of the disc. This evidence seems conclusive ; 

 but Mr. Huggins quotes, as additional evidence, the views of Dr. 

 Zollner respecting (i) peculiarities in the rate at which the 



