280 PROCEEDINGS OF THE AMERICAN ACADEMY. 



it was a fall, aud somewhat less when it was a rise, as one would 

 expect from the fact that the jacket was usually warmer than the air 

 surrounding it. The mean temperature of the jacket probably differed 

 in most cases less than 1° C. from the temperature of the double fun- 

 nel, yy, which it almost completely sun-ounded. The space around 

 h h and // h' beneath the jacket, and the lower part of the jacket itself, 

 was protected l)y a thick layer of cotton wool. The flat top of the 

 jacket and the plugs and wires above it were protected in the same 

 way. Under these conditions, the cooling or heating of the water by 

 radiation or absorption at its envelopes betweenji and^o '^^'^.s probably 

 exceedingly small. As a further precaution against error from this 

 source (and from certain other possible currents due to chemical ac- 

 tion at jx and^aj ^oi" instance), the stream passing through the upper 

 chambers of the apparatus and over the upper surface of the disk was 

 alternately made warmer and colder than the stream passing across 

 the under surface of the disk. 



The water-jacket J J was open to the air at A to allow the escape 

 of air-bubbles, which would otherwise have accumulated to such an 

 extent as to affect the flow of water at 0. Another outlet, at E, 

 served as an overflow when the water came too fast to be delivered 

 wholly through O. The streams from and E were joined in the 

 flask F, Figure 5. These minutiae are of much importance, as the 

 need of great uniformity in the rate of flow is imperative. 



The general arrangement of the apparatus, with the exception of 

 the electrical appliances, is shown in Figure 5. H^^ He,, //;, and H^ 

 are very effective contrivances * for heating a stream of water by the 

 combustion of gas, which is supplied at constant pressure through two 

 gasometers G^ and G>>, one of which is shown in section. The water, 

 which came from a large tank at the top of the Laboratory, with 

 great regularity of flow when uninterrupted by obstructions in the 

 apparatus, and at a nearly constant temperature, passed through the 

 three heaters, H^, H^, and H.^ without division. Between H^ and IT^ 

 the stream divided, one part, about one half, going through Hi to the 

 standpipe S^, the other part going without further heating to the stand- 

 pipe »S'i. These standpipes. from which a continual small overflow was 

 maintained, had the double function of maintaining a constant head for 

 the flow of the two streams through the conduction apparatus, and sift- 

 ing out much of the air, which the heating had driven out of solution 



* Made by the Buffalo Dental Manufacturing Company, No. 347 of their 

 Catalogue for 1895. 



