238 



Intelligence and Miscellaneous Articles. 



remarks on the circumstance as being what might be expected to 

 result from the reflecting surface being gaseous ; and he appears 

 to think that the polarimeter may afford us some information on 

 the question of the existence of a lunar atmosphere*. 



During the years 1872-75 we have at intervals made a rather 

 extended series of measurements with the polarimeter, of which 

 several different forms were tried, but one differing in little from 

 Arago's was found the more satisfactory. 



Although from a series of sixteen readings of the inclination of 

 the plates of parallel glass a value may be obtained for the polari- 

 zation on each night with a probable error of observation not ex- 

 ceeding 1 per cent., from some cause not yet established the dis- 

 crepancies between the various nights' work are much larger, and 

 the results must be accepted with reserve and regarded as only 

 provisional. 



The most probable values for the polarization (P), meaning by 

 that term the proportion between the intensities of the components 

 of the light polarized in and perpendicular to the plane passing- 

 through the sun at the several elongations (E), are for Mare 

 Crisium — 



E= 



P=l-r 



E = 



P=l-^ 







60 



0-830 



o 



110 



840 



70 



0-815 



120 



0-890 



80 



0-795 



130 



0-930 



90 



0-785 



140 



0-965 



100 



0-805 



150 



0-980 



Similar but less numerous measures than those on which the 

 above table is based were made for Mare Imbrium, Mare Sereni- 

 tatis, Palus Somnii, and the region between Macrobius and Proclus 

 and other parts. The polarization varies with the situation and 

 with the nature of the surface, being in general greater on the 

 plains than on the more uneven parts. 



Measurements of the light of the planet Venus made between 

 1872, March 12 and April 6, gave a mean value for the polarization 

 of 0-925, of which no regular variation was perceived during the 

 progress of the observations, although the change of phase which 

 occurred during the interval was considerable. 



May 15, 1877. 



GLASS-ENGRAVING BY ELECTRICITY. BY M PLANTE. 



I have previously described an experiment in which a glass tube, 

 through which passes a platinum wire serving as electrode to a 

 powerful galvanic current, was found to be instantaneously hollowed 

 out in a conical or tunnel-shape within a voltameter containing a 

 saline solution. In other experiments, on the luminous effects pro- 



* Arago, CEuvres, nouv. ed. par Barral, livr. xiv. chap, vi., t. ii. p. 101 &c. 



