Changes that happen to the fixed Stars . 187 
A method of ascertaining the quantity or intenseness of solar 
light might be contrived by some photometer or instrument 
properly constructed, which ought probably to be placed upon 
some high and insulated mountain, where the influence of va- 
rious causes that affect heat and cold, though not entirely re- 
moved, would be considerably lessened. Perhaps the thermo- 
meter alone might be sufficient. For though the lustre of the 
sun should be the chief object of this research, yet, as the ef- 
fect of light in producing expansion in mercury seems to be 
intimately connected with the quantity of the incident solar 
rays, it may be admitted that all conclusions drawn from their 
action upon the thermometer will apply to the investigation 
of the brilliancy of the sun. And here the forms laid down by 
Mr. Mayer, in his little treatise De V ariationibus Thermometri 
accuratius definiendis * may be of considerable service to dis- 
tinguish the regular causes of the change of the thermometer 
from the adventitious ones, among which I place the probable 
instability of the sun's lustre. 
Introductory Remarks and Explanations of the Arrangement and 
Characters used in the following Catalogue. 
This catalogue contains nine constellations, which are ar- 
ranged in alphabetical order. I have called the present col- 
lection the first catalogue. The rest of the constellations, 
which are pretty far advanced, will be given in successive small 
catalogues as soon as time will permit to complete them. 
Each page is divided into four columns, the first of which 
gives the number of the stars in the British catalogue of Mr. 
Flamsteed, as they stand arranged in the edition of 1725. 
* Tobies Mayeri opera inedita, I. 
Bb 2 
