The results he ultimately arrived at were, that the yellow and red stars of the IInd and IIIrd types twinkle less rapidly than the white stars of the Ist type. Whilst the average number of scintillations per second of the stars of type III. were 56, those of type II. were 69, and those of type I. 86. These differences may be confidently said to depend upon too many observations of too many different stars to be fortuitous. Montigny also arrived at a number of incidental conclusions of considerable interest. The one main thread running through them, is that there is a connection between the twinkling of a star and its spectrum, which had never before been thought of. We are justified, indeed, in going so far as to say, that Montigny’s observations point distinctly to a law on this subject, the law being that the more the spectrum of a star is interrupted by dark lines, the less frequent are its scintillations. The individual character of the light, therefore, emitted by any given star appears to affect its twinkling, both as regards the frequency thereof and the colours displayed.
Montigny collected some other interesting facts with reference to twinkling, which may here be stated in a concise form. There is a greater display of twinkling in showery weather, than when the atmosphere is in a normal condition; and in winter than in summer, whatever may be the weather. In dry weather in Spring and Autumn the twinkling is about the same, but wet has more effect in Autumn than in Spring in developing the phenomenon. Variations in the barometric pressure and in the humidity of the air also affect the amount of twinkling; there is more before a rainy period, likely to last 2 or 3 days, than before a single, or, so to speak, casual rainy day. Twinkling also varies with the aggregate total rain-fall of any group of days, being more pronounced as the rain-fall is greater, but decreasing suddenly and considerably as soon as the rainy condition of the atmosphere has passed away. The number of scintillations found to be observable with the aid of Montigny’s instrument (which he called a “_scintillomètre_”), varied from a minimum of 50 during June and July, to 97 in January, and 101 in February, increasing and decreasing in regular sequence from month to month. When an Aurora Borealis is visible, there is a marked increase in the amount of twinkling. It would be interesting to follow up this last named discovery by an endeavour to ascertain whether the fluctuations which are coincident in point of time with an Auroral display depend upon optical considerations connected with the Aurora, or on physical considerations having any relation to the increased development of terrestrial magnetism.