210 REPORT — 1855. 



which the dividing of the drum cannot be avoided, tlie greatest possible care ought to 

 be taken in effecting a correct and secure union of the two parts. He had on some 

 occasions diminished very materially the inconvenience arising from vibrations of the 

 arm, by connecting a spring balance with tlie scale for bearing the weights, in such a 

 way as to make the arm tend to stable equilibrium in the position intended for it 

 when working. 



It very frequently happens that, from no clearly apparent or controllable cause, a 

 violent torsional tremor occurs in the friction drum and driving shaft ; while through 

 some very slight change of circumstances, such as a change in the heat of the drum, 

 or in the mode of application of the water, or in the speed of revolution of the shaft, 

 steadiness of motion maybe instantly restored, and perhaps soon again destroyed. 

 The origin of the tremor he attributes to one of the known laws of the friction and 

 cohesion of bodies ; namely, that the force necessary to overcome the cohesion before 

 sliding has commenced, is usually more than the force necessary to overcome the 

 friction of the sliding motion. The evil liable to arise from the tremor he had found 

 to be very great, the danger to life of the by-standers in such experiments being 

 sometimes considerable. He had himself witnessed a case in which a violent tremor 

 occurred in the testing of a powerful water-wheel ; and, on the conclusion of the ex- 

 periments, the working shaft of the wheel was found to be split and twisted. 



Notwithstanding the difficulties occasionally arising in the use of the friction 

 dynamometer, however, its remarkable efficiency, when not marred by such occurrences, 

 and the certainty of its indications when working properly, render it a most valuable 

 apparatus for practical use in many important and delicate cases often arising for 

 decision. It is therefore a mechanism in which improvements are much to be desired ; 

 and also in which, he is of opinion, they are likely to be found. 



On a Centrifugal Pump and Windmill erected for Drainage and Irrigation 

 in Jamaica. By James Thomson, A.M., C.E., Belfast. 

 In this paper Mr. Thomson gave explanations, with the aid of large drawings, of a 

 centrifugal pump recently constructed, embodying the improvement of an exterior 

 whirlpool which he had first made public in the Mechanical Section at the Belfast 

 Meeting in 1852. He also described a windmill with its framing of very simple con- 

 struction, which had been specially designed for working the pump. The apparatus 

 ■was prepared for purposes of drainage and irrigation in Jamaica, the costliness of 

 fuel and the habitual use of windmills in that island having led to the selection of the 

 windmill in this case as the source of power. The whole apparatus was constructed 

 in Glasgow and afterwards erected and brought into action at its destination. 



On an Jndia-ruhber Valve for Drainage of Loio Lands into Tidal Out- 

 falls. By James Thomson, A.M., C.E., Belfast. 



In this paper Mr. Thomson described a valve, composed of a flap of vulcanized 

 india-rubber closing against a perforated plate, which he had introduced on a water- 

 course of the Belfast Water-works. This valve on trial had proved to accomplish very 

 efficiently the purpose for which it was intended, and which required that it should 

 open and close with the most perfect freedom, should keep water-tight when close, and 

 should not be liable to be hindered from closing properly by the accidental interposi- 

 tion of a small piece of stick or other floating object. 



It was with a view to the introduction of valves of similar construction or of like 

 principle for the discharge of water into tidal outfalls in the drainage of fens, that' 

 Mr. Thomson thought the subject worthy of the attention of the Mechanical Section. 

 Vulcanized india-rubber valves had in late years, as was well known, been used for 

 many purposes, and in many different forms with great advantage ; but he was not 

 aware of any cases of their employment in the manner or for the purpose he now 

 proposed. 



On Practical Details of the Measurement of Running Water by Weir 

 Boards. By James Thomson, C.E. 



