YIBGINIS BY THE MOON. 183 



torn should have twinkled more than on a summer night, and as I 

 said before, should have appeared with diminished lustre. 



In order to satisfy myself whether I was mistaken in my opinion, 

 I wrote to Mr. Chalmers, I\R.A.S., who resides at Barrie, to as- 

 certain whether he had also seen the appearance I have attemped to 

 describe. His reply corroborates what I have said; and also 

 introduces the subject forming the second part of this paper, viz. 

 the occupation of Spica by the moon, which it was my intention 

 to have observed, but which intention I was unavoidably prevented 

 from carrying into effect. I will now submit to the Institute, that 

 portion of Mr. Chalmer's reply which refers to the subject matter 

 of this paper. 



Mr. Chalmers says, " I did observe the planetary appearance of one 

 star of the 1st magnitude as you describe, by mere chance. It 

 was a very cold night, the 12th, (at least here,) but I happened to be 

 up late, and before going to bed I had a look at the moon with the 

 naked eye ; I then saw that Spica Virginis would be occulted, and I 

 waited up for it. I extract the notes I made at the time: 13th 

 March, 1-2 a m., mean time, Barrie; Spica Virginis occulted by the 

 moon, the star was actually projected on the moon's disc, as I could 

 distinctly see the edge of our satellite outside the star ; the star then 

 disappeared instantaneously, not gradually, but as if it had been ex- 

 tinguished in a moment. The atmosphere was perfectly clear, with a 

 sharp frost ; the star did not appear to suffer any diminution of light, 

 and was occulted at the bright edge of the moon ; — curious planetary 

 appearance of the star — telescope used three and a half foot, by Dol- 

 lond — definition excellent. The occultation of Spica as seen at 

 Barrie, being a subject of far greater interest than my own observa- 

 tions on the night in question, I shall proceed at once to offer to 

 the notice of the Institute, some remarks made by eminent 

 authorities on the way in which stars have been seen either to hang 

 as it were upon the moon's disc, be projected on it, or reappear and 

 disappear along the edge of the moon, in occultations. 



Arago saw, during a total eclipse of the moon, a star distinctly 

 adhere to the slightly luminous disc of the moon during the 

 conjunction. Humboldt says, those cases in which it has been 

 asserted that a disappearance and reappearance and then a re- 

 peated disappearance, have been observed during an occulta' 

 tion, may probably indicate the ingress to have taken place 

 at a part of the moon's edge, which happened to be deform- 

 ed by mountain declivities and deep chasms. Lardner says : 

 some observers of sufficient weight and authority to command gene- 



