fome 'Thermometr'ical Experhiients. 523 
that i° of heat, according to Fahrenheit’s thermometer, 
increases the bulk of a quantity of quickfilver of T75 .^^ ths 
parts, viz . if the bulk of a quantity of quickfilver in the 
temperature of 50° is equal to 100,000 cubic inches, the bulk 
of the fame quantity of quickfilver in the temperature of 51 0 
will be equal to 100,009 cu hic inches. 
It is almoft fuperfluous to mention, that the cavity of the 
tubes employed for thefe experiments, muft be perfectly uni- 
form throughout. The fcafes to be u fed for this method 
fhould be fo exact as to be turned by the hundredth part of a 
grain when charged with about half an ounce weight. 
From thefe obfervations the method of graduating, or of 
determining the length of a degree in a new thermometer, is 
eafily deduced, the only requifites for the calculation being the 
weight of a quantity of quickfilver, which fills a known 
length of the tube, and the weight of the whole quantity of 
quickfilver contained in the thermometer when filled* Sup- 
pofe, for inftance, that in making a new thermometer i it 
be found, that the weight of fo much quickfilver as, fills five' 
inches length of the tube is equal to ten grains, and that, the 
weight of the whole quantity of quickfilver contained in the' 
thermometer weighs 300 grains. It is plain, that ^ if the 
whole quantity of quickfilver weighs 300 grs. parts 
of it muft weigh 0,027 8 T * £>iit the weight qf .fo much; mer- 
cury as fills five inches of the tube is equal to iPSgraih.s<; 
therefore, 0,027 gr. weight, of quickfilver muft fill 0,0133 
inch of the tube, and this is equal to the. length of 1 °, or ther 
double, treble, &c. of it is. equal to two, three, &c. degrees.; 1 
By this means the fcale may be made ; that is, it , m-ay, ben 
divided into degrees, but the numbers cannot be added tp them . 
without finding which of thofe degrees correfponds with the 
5 freezing 
