late Professor of' Practical Astronomy in Glasgow. 9 



ments, by the slow vibrations of such a pendulum, which in- 

 duced Mr Wilson to prosecute these experiments. 



Not long after this, he also put in execution a remarkable 

 improvement of the thermometer, which consists in having the 

 capillary bore drawn very much of an elliptical form, instead 

 of being round. By this means the thread of quicksilver upon 

 the scale presents itself broad, and much more visible than it 

 does in a cylindrical bore of the same capacity. The difficulty 

 of constructing thermometers of this kind had nearly hinder- 

 ed him from completing his invention, as the thread of quick- 

 silver was found extremely liable to disunite when descending 

 suddenly in so strait a channel. But, by his long experience, 

 joined to farther investigation and more trials, he at last dis- 

 covered a method of blowing and filling thermometers with 

 flattened bores, which freed them entirely from this defect. 



About the same time, also, he conceived the design of con- 

 verting a thermometer graduated for the heat of boihng-water, 

 into a marine barometer, in consequence of the well-knov/n dif- 

 ference of temperature which water, when boiling, acquires un- 

 der the variable pressure of the atmosphere. This he effected, 

 by making a boiling-water thermometer, about a foot in length, 

 with a pretty large ball, and having a thread of quicksilver 

 as broad and visible as was consistent with a very perceptible 

 run upon small alterations of temperature. The stem of this 

 thermometer he fortified, by inclosing it in a cylindrical case 

 of white iron, having soldered to it, at its lower end, a socket 

 of brass for receiving half of the ball, which afterwards became 

 entirely defended, by screwing to the socket a hemispherical 

 cap. At the other end of the case which environed the stem, 

 there was soldered a tube of brass, wide enough to admit a 

 scale of proper dimensions, before which there was an opening 

 in the tube, defended by glass. 



The utmost range of the scale he determined by the points, 

 where the thermometer was found to be stationary when the 

 ball, and a certain part of the stem were immersed in water, 

 boiling under the greatest variations of pressure which the 

 climate afforded. The interval so found, he subdivided by 

 other observations into degrees, which corresponded to inches of 

 the barometer, and which were so denominated upon the scale. 



