V 



glass, he pointed out that the eapillary film of water between the slabs 

 draws them together with not inconsiderable mutual pressure, and 

 hence the freezing. Thomson further showed that when two pieces of 

 ice are brought to touch each other at a point wholly immersed under 

 water, and thus free from capillary action, the most minute pressure 

 pushing the two together causes the growth of a narrow connecting 

 neck, which may be made to grow by continued application of the 

 pressure ; while the application of the smallest force tending to draw 

 the two asunder causes the neck to diminish in thickness, and finally 

 to disappear. 



In later years James Thomson further developed the theory of 

 1849. He showed that stresses, of other kinds than pressure equal 

 in all directions, can relieve themselves by means of local lowering of 

 the freezing point in ice ; and he showed, by theory and by experi- 

 ment, that the application of stresses may assist or hinder the growth 

 of crystals in saturated solutions. Som^ of these conclusions are of 

 such importance that they deserve to be better known. The title of 

 the paper in which the last-named results were given is, " On Crystal- 

 lisation and Liquefaction as Influenced by Stresses tending to Change 

 of Form in the Crystals,"* 1861. It included the amended and 

 extended theory of the plasticity of ice. 



In 1850, James Thomson was engaged in perfecting his design for 

 the Vortex water-wheel. He had soon some orders for the wheel ; and 

 in 1851 he took the important step of settling down as a civil en- 

 gineer in Belfast. 



His business grew by degrees. His health improved, and we find 

 him occupied in the next two or three years with scientific investiga- 

 tions as to the "properties of whirling fluids." This led to improve- 

 ments in the action of blowing fans on the one hand, and, on the 

 other, to the invention of a centrifugal pump and to improvements in 

 turbines which were described to the British Association at Belfast 

 in 1852. At this meeting, also, he described " A Jet Pump, or 

 Apparatus for drawing up Water by the Power of a Jet " ; and these 

 investigations led to the designing, on the large scale, of pumps of 

 this kind. Some of these pumps have done important work in the 

 drainage of low lands at places where a small stream, capable of 

 supplying the jet, can be found in the immediate proximity. His 

 investigations on the mechanics of whirling fluids, again, led to the 

 design of great centrifugal pumps, the largest of which are now at 

 work on sugar plantations in Demarara. 



It will thus be seen that he was giving much attention to water 

 engineering ; and in November, 1853, he became resident engineer 

 to the Belfast Water Commissioners, a post which he occupied till the 

 end of 1857. 



* ' Eoy. Soc. Proc.,' Dec. 5, 1861. 



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