776 Transactions of the Ait eric an Institute. 



gets lower than the top of the tube, the difference of level of the 

 water is balanced by a difference of level in the mercury about 1-1 3th 

 part as great ; and this is multiplied upon the scale in proportion to 

 the reduction of the tube; so that the scale can be made of any 

 desired length. 



The President — I have never seen anything like this in the books, 

 and it strikes me as a remarkable combination. The tube in the 

 boiler will always be kept full, by the condensation of the steam. 



Dr. Tan der Weyde — This resembles a barometer which I have 

 seen in Europe. It is a syphon barometer, and to the lower cup 

 is attached a small tube, filled with a colored fluid. In this way 

 the scale may be enlarged to the whole length of the barometer. 

 Glycerine, which will not evaporate, may be employed in this tube. 



Mr. J. K. Fisher — For my own use, I would prefer not to have 

 the enlargement of the scale. One-thirteenth of an inch, for an inch 

 of water, is sufficient for practical use. But this would be useful in 

 the office of the captain or chief engineer. The more of these tell- 

 tales there are about, the more watchful the engineer will be. 



Dr. Yan der Weyde — The mercury gauge is there, and there must 

 be this syphon. It will do no harm to put in the colored fluid, and 

 then you can look at which you please. 



Mr. E. Weir described Massey's Low- water Detector, which admits 

 steam to a pipe, and expands it, blowing a whistle when the water 

 reaches a point too low for safety. 



The President suggested that this gauge might be made self-record- 

 ing, like Edson's Steam-pressure Gauge. 



Mr. R. Weir suggested that a modification of this instrument might 

 be applied to registering the tides. 



The following paper was then read : 



A Hypothesis Relating to Heat. 

 By Prof. P. H. Van dek Weyde. 

 I propose to commence my remarks to-night with a theory, and 

 then to explain a new hypothesis, which will illustrate the difference 

 between a theory and a hypothesis. Gravitation is not a theory ; it 

 is a stubborn fact. The law of gravitation, that it increases in inverse 

 ratio with the square of the distance, is as much a mathematical 

 necessity as that the sum of the three angles of a plane triangle equals 

 two right angles. It may not seem a necessity to a mind not familiar 

 with mathematical truths ; but it is no less a necessity in fact, that 

 any force coming from a point and diffusing itself into space, must 



