TIDAL OBSERVATIONS. 275 



First Report of the Committee, consisting of Dr. Joule^ Prof. Sir W, 

 Thomson, Prof. Tait, Prof. Balfoue Stewart, and Prof. Maxwell, 

 appointed for the purpose of determining the Mechanical Equivalent 

 of Heat. 



We are able to report that progress has been made with the experiments 

 iindertakeu by Dr. Joule on behalf of the Committee. Friction of water is 

 the method he has employed ; and the average result of upwards of sixty 

 experiments is 773-1 in British gravitation units at Manchester, the greatest 

 deviation from the above average being ^1^. 



Experiments * have yet to be made on the capacity for heat of the brass 

 of which the calorimeter is constructed, which has provisionally been calcu- 

 lated from the results of Regnault for this alloy. The greatest possible error 

 which may have arisen in this way is believed to be 75-1^. Dr. Joule also 

 proposes to compare his mercurial thermometers with the air-thermometer, 

 with a view to obtain accurate boiling-points, and thus correct values of the 

 thermometric scale. The greatest correction which it may be found needful 

 to apply on this account amounts to about -j-i-^. These maximum corrections, 

 if taken in the same direction, would necessitate the addition of 4-5 to the 

 equivalent above named. 



The experiments made by Hirn on the friction of water have led him to 

 the number 786. But the average of his results, derived from the friction, 

 boring, and crushing of metals, gives 77-A. 



Assuming that the above experiments and those made by Dr. Joule for the 

 Committee on Standards of Electrical Resistance are to be relied on, the unit 

 issued by it would appear to have a resistance too small by -^. 



The Committee are happy in being able to state that Professor Maxwell 

 has been working some time with a view to the redetermination of this unit, 

 and that he has also undertaken fresh direct experiments for determining the 

 dynamical equivalent of the thermal unit. 



Report of the Committee appointed for the purpose of promoting 

 the extension, improvement, and harmonic analysis of Tidal Obser- 

 vations. Consisting of Sir William Thomson, LL.D.,F.R.S., Prof. 

 J. C. AvAus, F.R.S., J. Oldham, William Parkes_, M.Inst. C.E., 

 and Adnairal Richards, 7?. A'., F./?.S. Draiv mj9 6?/ Sir William 

 Thomson. 



Since the publication in 1873 of the Committee's Report for 1872, a large 

 amount of work has been gone through, in the way of harmonic analysis, ex- 

 hausting the funds at the disposal of the Committee for this purpose, but none 

 of the results have hitherto been published. They are now offered for pirbli- 

 cation in this final Report of the Committee, and along with them, by permission 



* [These experiments, up to the present date, sliow a smaller capacity than that antici- 

 pated, bringing up the equivalent to 77-t-l, which will be subject to a small correction, 

 possibly amounting to jjn, on acsount of the thermometric scale error. — Note, November 

 13, 1876. -J. P. J.] 



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