562 EEPOET— 1887. 



Further investigation will doubtless explain this, and also determine the 

 best proportional depths. From my present experience, in constructing 

 another model, I should adopt a somewhat greater exaggeration of the 

 vertical scale. In the meantime I have called attention to these results, 

 because this method of experimenting seems to afford a ready means of 

 investigating and determining beforehand the effects of any proposed 

 estuary or harbour works ; a means which, after what I have seen, I 

 should feel it madness to neglect before entering upon any costly under- 

 taking. 



I have only to say that, as it was not practicable to exhibit the model 

 to the Section, I have had it working in the new engineering laboratory 

 through the college. Unfortunately it could not be started before 

 Monday, and it will not yet have run more than 1,000 tides, since the 

 sand was put in flat, so that it is not probable that the regime is yet quite 

 stable ; still the principal features have come out. 



Experiments on the Mechanical Equivalent of Heat on a large 

 scale. By E. A. Cowper and W. Anderson. 



[A communiuutioa ordered by the General Committee to be printed in extenso 

 among the Reports.] 



[Plate X.] 



The extremely interesting experiments of Dr, Joule on the mechanical 

 equivalent of heat, led one of the authors of the present paper, some years 

 ago, to speculate on the possibility of conducting such experiments on a 

 much larger scale. 



It appeared that it would be possible to employ a powerful machine 

 that would absorb a large amount of power, and to keep it continually 

 going for a whole day at a time, so as to get everything into a thoroughly 

 nQrmal state, and so arrange matters as to eliminate all loss or gain from 

 radiation or conduction. The first idea was to employ an india-rubber 

 masticating machine, which would absorb a vex'y large amount of power 

 in a small space, and to enclose it in a small tank, and that again in a 

 larger tank, and then run cold water into the machine, and let the hot 

 water from it run into the small tank, so as to entirely surround the 

 machine with hot water of the same temperature as the water coming 

 out, and then let the water from the first small tank flow into the larger 

 tank, and from that to waste, the outside tank being kept up to the 

 same temperature as the inside tank and the machine, so that the machine 

 should neither lose heat nor absorb it. However, after much considera- 

 tion, it was thought best to employ one of the late Mr. Fronde's dynamo- 

 meters, such as he used for trying the power of marine engines, though 

 on a smaller scale. Accordingly, through the kindness of Messrs. Heenan 

 and Froude, the loan of such a dynamometer was obtained and fitted up 

 at Erith as above indicated, viz., with a small tank inside a larger one, 

 which last was made of thick wood and well lagged outside with three 

 thicknesses of hair-felt ; and this provision was found in practice to be so 

 efficient that the tank of water only lost two degrees in I65 hours when 

 standing, or about one degree in 8j hours. 



