8^ Intelligence and Miscellaneous Articles. 



ing the attention of astronomers to one of my memoirs upon instru- 

 mental errors, in which I have incidentally treated of eclipses*, it 

 may perhaps not be considered amiss for me again to dwell upon 

 the notions which I published last year. 



In accordance with these notions, it would be of importance to 

 determine the temperature of the atmosphere, and especially its 

 variations, by means of very delicate thermometers, and at different 

 elevations above the surface of the earth. If even aeronauts would 

 consent to make an aerial ascent on the 28th of July, they would un- 

 doubtedly enjoy during the complete eclipse, a very beautiful spec- 

 tacle ; they would be certain, at all events, to render their under- 

 taking of great scientific interest, by carefully determining the vari- 

 ations of the temperature at an elevation of some thousands of metres. 

 Probably some very useful information upon the temporary constitu- 

 tion of the atmosphere during the eclipse might be obtained by mea- 

 suring several very exact zenithal distances of the sun or the moon, 

 before, during, and after complete obscuration. M. Otto Struve 

 has informed me that arrangements will be made, at least at one 

 station, in conformity with the plan suggested by me, and this 

 good new^s diminishes my regret at not being able to render my 

 feeble cooperation in this noble astronomical undertaking. I may, 

 however, be permitted to recall to the attention of observers a 

 phaenomenon which the Report of the British Association has omit- 

 ted to notice, undoubtedly because the phaenomenon has appeared 

 too doubtful or completely exceptional. But as numerous stations 

 ought to be arranged in several lines perpendicular to the progressive 

 motion of the shadow, and as the observers ought to occupy every 

 possible position within the cone of the shadow, it is probable that 

 no phaenomenon, however rare and exceptional, will escape attention 

 when so scientifically directed. I must say a few words here upon 

 the brilliant points observed by UUoa and M. Valz upon the disc of 

 the moon. In consequence of an inherent tendency of the mind, 

 which at first always attributes substance and reality to appearances 

 by which it is struck, the luminous points have been explained as 

 material apertures existing in the substance of the moon. But in 

 my opinion, one and the same theory is sufficient to explain both the 

 external protuberances and the internal apertures ; this consists in 

 viewing them as two distinct effects of mirage produced temporarily 

 in the atmosphere ; and I have pointed out the probable connexion 

 of these phaenomena, which are so dissimilar in appearance, in the 

 excellent Astronomical Journal of my learned friend Mr. Gould, 

 published in the United States f. They both depend upon the distri- 

 bution of the temperatures of the layers of air parallel to the visual 

 rays ; except that in the second case, and in consequence of the posi- 

 tion of the observer, the trajectory presents a point of inflection which 

 does not exist in tlie case of the external protuberances. These 

 statements are very reservedly made ; as regards the fact itself, it is 

 based upon evidence, the entire value of which is known to astrono- 

 mers. M. Valz must himself have been forcibly struck by it, for 

 during the occurrence of a partial eclipse here, I have seen him care- 

 fully seek for the brilliant aperture which he remarked in 1842. 



* Comptes Rendus, 1850, Nov. 4. 



t Gould's Astronomical Journal, No. 20, p. 167. 



