2 1 6 SECTION ME CHANICS. 



meter, by which it will be possible to obtain continuous records of 

 the diurnal changes in the attraction of the sun and moon as in- 

 fluencing the tides. This instrument belongs, however, rather to the 

 domain of physics than to that of mechanical science. 



These general remarks upon the subject of measurement may suffice 

 to call your attention to its importance, several branches of which, those 

 of Linear, C^lbical, and Electrical Measurement, will now be dealt with. 



The discussions which will follow these addresses will be carried on 

 under circumstances such as have never before co-operated, namely, 

 the presence of leading men of science of all civilised nations, who 

 will take part in them, and the easy reference which can be had to 

 the most comprehensive collection of models of scientific apparatus 

 both of modern and ancient which has ever been brought together. 



Mr. BRAMWELL, C.E. : I think it is our duty to move a vote of 

 thanks to Dr. Siemens, our President, for his interesting and valuable 

 address to our conference to-day. He has foreshadowed a large 

 amount of work, which I hope will be faithfully fulfilled, and if so I 

 am sure these meetings will be most useful to mechanical science. 



Sir JOSEPH WHITWOE^TH : I shall be most happy to second that. 



The motion was carried unanimously. 



The PRESIDENT : I thank you very much for your expression of 

 approval with regard to the address that I have just delivered. I 

 found the subject was a very vast one, and that it was impossible to 

 do full justice to it, but I hope that this address may be followed now 

 by communications of a more specific kind, which will be both 

 interesting and useful. I will now call on Sir Joseph Whitworth to 

 read his communication 



ON LINEAR MEASUREMENT. 



Sir JOSEPH WHITWORTH : The two great elements in mechanics 

 are the power of measurement and the true plane. The measuring 

 machines which I have constructed are based upon the production of 

 the true plane. 



Measures of length are obtained either by line or end-measurement. 



The English standard yard is represented by two lines drawn across 

 two gold studs sunk in a bronze bar about 38 inches long, the 

 temperature being at 62 fah. 



