SCIENCE. 



[N.S. Vol. XVI. No. 414. 



Carolina for the first time. To get the eggs 

 of P. ciliata the following method was used: 

 A horse was driven into a low place inhabited 

 by these insects and from him specimens loaded 

 with blood were transferred to a jar. They 

 were then put into a tin bucket with a little 

 water in the bottom and covered with netting. 

 They were fed daily with blood from the hand, 

 and after about five days their eggs were 

 found in the water. The eggs lie separately, 

 like those of Anopheles. Contrary to expecta- 

 tion and report, Anopheles was found breed- 

 ing abundantly in a barrel. 



Dr. J. E. Duerden gave an account of his 

 work on ' Boring Algse as Agents in the Dis- 

 integration of Corals.' The corolla of about 

 thirty species of West Indian corals, decalci- 

 fied in the course of a morphological study 

 of the polyps, all yielded a fluflly mass made 

 up of filamentous algas. The algse were pres- 

 ent in greatest number and variety in the 

 older dead parts of corals, especially in so- 

 called ' rotten coral,' but were also found 

 throughout the part of the skeleton directly 

 clothed with the polypal tissues, the only ex- 

 ception being at the tips of rapidly growing 

 branches. The filaments occurring most fre- 

 quently belong to two species of green algse 

 and a red alga; where present in quantity the 

 former give a green color to the freshly 

 macerated corallum, and the latter a pink 

 tinge. Similar boring algse were also ob- 

 tained from many Pacific corals. 



The algse attack the calcareous skeleton of 

 corals in the early stages of development, and 

 their ramifications keep pace with its growth. 

 Penetration of the hard coral is evidently 

 affected by chemico-physical means, and their 

 presence in such abundance results in a serious 

 corrosive action, both superficially and intern- 

 ally; when assisted by other boring organisms, 

 such as sponges and moUuscs, it must lead to 

 the rapid disintegration of dead coral blocks. 

 Attention was drawn to the bearing of such 

 disintegration upon the various theories asso- 

 ciated with the formation of coral reefs. 

 Chas. Baskeeville, 



Secretary. 



DISCUSSION AND CORRESPONDENCE. 



THE KINETIC THEORY AND THE EXPANSION OF A 

 COMPRESSED GAS INTO A VACUUM. 



Mr. Fireman, in his reply to my note re- 

 garding his communication to the American 

 Association, states that I misread his abstract, 

 and that it was on this account that I failed 

 to understand its contents. 



My difficulty was not in imderstanding the 

 contents, but in imderstanding how they ex- 

 plained the facts, or why this picturesque 

 conception of a sorting out of the fast and 

 slow molecules without the aid of Maxwell 

 demons, was in any way deemed necessary to 

 the explanation of the heating and cooling 

 of the gas. 



Neither Natanson's elaborate quantitative 

 treatment nor what Mr. Fireman calls his 

 simple qualitative explanation appears to be 

 necessary to account for the heating and cool- 

 ing in the two receivers, in spite of Mr. Fire- 

 'man's assertion that the explanation com- 

 monly given is unsatisfactory. 



Mr. Fireman appears to have overlooked the 

 fact that, when a compressed gas passes from 

 a receiver into an exhausted chamber, there 

 is, in addition to the molecular motion, a 

 motion of the gas as a whole, i. e., a mass of 

 the gas is given a motion of translation, which 

 is superimposed on the molecular motion. 



To originate this motion requires an ex- 

 penditure of energy, and a consequent lower- 

 ing of temperature results. The matter is 

 fully treated in the works of Clausius, Max- 

 well, Kelvin and Meyer, where it is shown 

 that when a mass of gas is set in motion by 

 its own expansion, the mean molecular ve- 

 locity becomes less and the temperature is 

 lowered; since the mean velocity is less, the 

 component of molecular perpendicular to the 

 direction of flow is less, and consequently the 

 pressure in this direction is less than in the 

 case of the gas at rest. This accounts for 

 the cooling in the compression chamber. 



The heating of the gas in the second re- 

 ceiver is to be referred to the same causes as 

 the heating of the gas under the piston in 

 the case of compression. 



Mr. Fireman has difficulty in understand- 

 ing how a higher average molecular velocity. 



