the Scintillation of the Stars. 223 
singular variations of brilliancy have so much surprised astrono- 
mers for the last thirty or forty years. Unfortunately this star 
is only visible at 31° north latitude ; and to observe it at a height 
of 30° above the horizon, one must travel as far as the equator, 
so that this research must be left to the astronomers of the other 
hemisphere. ‘ 
6th. Scintillation of the Planets. 
It is generally believed that the planets do not scintillate at 
all, or scarcely at all. Nevertheless I have often observed a 
sensible scintillation of Venus and Mars, and im a few rare cases 
I have also observed a slight scintillation of Jupiter and Saturn. 
For those persons who undertake to explain the phenomenon of 
the scintillation, it would be important to know if really the 
scintillation of these planets ever becomes very decided. 
I would therefore call the attention of observers who may find 
themselves under atmospherical conditions of a nature to render 
the general scintillation very strong, to this point, as they might 
perhaps be able to ascertain whether Jupiter and Saturn ever 
sensibly scintillate. 
7th. Accidental Observations. 
In order to complete the study of this phenomenon, excep- 
tional circumstances must not be neglected :—Among others, 
observations taken during an aurora borealis, both of the stars 
which appear plunged in the light of the aurora, and of the 
others in other parts of the heavens. During six years I have 
never been able to make any observations of this nature at 
Morges. 
The observation of the scintillation from the summit of a high 
mountain. De Saussure made several during the time he was 
on the “ Col du Géant ;” but those which are given in the works 
of this celebrated man are too few in number, and not detailed 
sufficiently to be able to draw from them any certain conclusions. 
Mr. Piazzi Smyth remembers that the scintillation appeared 
to him very feeble from the summit of the Peak of Teneriffe ; 
and during the time I was staying on the Great St. Bernard, 
I remarked that the general scintillation was always very feeble. 
Is this always the case ? 
8th. Accessory Observations. 
In order to render the observations on the scintillation really 
interesting and useful, it is important that they should be accom- 
anied by meteorological observations as complete as possible. 
At least let the state of the barometer, hygrometer, and thermo- 
meter be noted exactly; also the state of the heavens, and the 
force and direction of the wind. 
