2 ~ 6 Mr. Morgan’s Experiments to a (certain the 
times before the charge has made a fmall perforation in the 
bulb. If again a thermometer filled with mercury be inverted 
into a eiftern, and the air exhaufted in the manner I have de- 
fcribed for making the experiment with the gage, a Torricellian 
vacuum will be produced ; and now the ele&ric light in the 
bulb, as well as the fpark in the tube, will be of a vivid green; 
but the bulb will not bear a frequent repetition of charges be** 
fore it is perforated in like manner as when it has been ex- 
haufted by an air-pump. It can hardly be neceflary to obferve, 
that in thefe cafes the eledlric fluid afifumes the appearance of a 
fpark *, from the narrownefs of the pafiage through which it 
forces its way. If a tube,, 40 inches long, be fixed into a globe 
8 or 9 inches in diameter, and the whole be exhaufted, the eledric 
fluid, after paffing in the form of a brilliant fpark throughout 
the length of the tube, will, when it gets into the infide of the 
globe, expand itfelf in all directions, entirely filling it with a 
violet and purple light, and exhibiting a ftriking inftance of the 
vaft elafticity of the eleftric fluid. 
I cannot conclude this paper without acknowledging my obli- 
gations to the ingenious Mr. Brook, of Norwich, who, by com- 
municating to me his method of boiling mercury, has been the 
chief caufie of my fuccefs in thefe experiments +*. I have lately 
learned 
* By cementing the Iking of a guittar into one end of a thermometer tube, a 
fpark may be obtained as well as if the tube had been fealed hermetically. 
-}' Mr. Brook’s method of making mercurial gages is nearly as follows. Let a 
glafs tube' L (fee fig. 2.}, fealed hermetically at one end, be bent into a right.- 
angle within two or three inches of the other end. At the dillance of about an inch 
or lefs from the angle let a bulb (K), of about | of an inch in diameter, be blown 
in the curved end, and Let the remainder of this part of the tube be drawn out (I) 
- ' - . • A , fo 
