542 PROFESSOR DANIELL ON THE WATER-BAROMETER ERECTED 
thermometer ( c , d) which had been made for the purpose, with a platinum scale 
carrying a spring of the same metal upon its back, was pushed down into the 
tube to a situation where it had been calculated it would always be immersed 
in the water, notwithstanding its oscillations ; and where a slight tapering of 
the tube insured its being fixed by the action of the spring. By a careful appli- 
cation of the blow-pipe the glass was now softened, and an external collar (g) 
pushed up upon it, about eight inches from its upper extremity. This was 
deemed necessary to give it additional support, and to prevent its slipping in 
its proper position. The upper extremity was then contracted and drawn out 
into a small tube six inches long and of about one quarter of an inch diameter. 
These preparations having been successfully completed, a small stop-cock 
was fitted to the upper end of the contracted tube by very careful grinding, 
and secured in its place by a little white lead. The tubes were then again 
packed in their case, and the cover screwed down. 
A small copper steam-boiler ( h,i ) was now constructed of what is called the 
waggon shape, and which was intended to form the cistern of the barometer. 
Without the cylindrical cover (ft, l ) it is eighteen inches long, eleven inches 
wide, and ten inches deep. Its bottom is slightly arched ; and towards one 
extremity on the inside is fixed a small cylinder (m,n) six inches high and 
three inches diameter ; the object of which is to form a receptacle into which, 
the lower end of the tube being made to dip, the great body of the water might 
at any time be drawn out of the cistern, if required, without, for a short time, 
disturbing the water in the tube, or allowing any air to ascend into the vacuum. 
A small hole (o) was afterwards drilled in this cylinder, which is six inches from 
the crown of the arch, and four inches and a half from the bottom ; so that the 
water might be more completely withdrawn. At the other extremity is a 
cock (p) for drawing it olfi, if at any time it should be necessary to change it. 
The cover (ft, l) is an arch of the height of six inches. Immediately over the 
cylinder above described, a length of five inches (ft, q) is fixed and fitted with 
a stuffing-box for the glass tube to pass through. Beyond this it is made to 
take off, but may be fixed down by means of screws : on the summit of this 
moveable end a cock (s) is placed. The whole of the interior has been strongly 
tinned. 
Everything being now prepared, the steam-boiler was set with brick-work 
