May 5, 1899.] 



SCIENCE. 



659 



and needs no introduction to the scientific 

 world. 



Beaufoi'fc is situated near one of the great 

 ocean inlets, and the waters of the harbor and 

 adjacent sounds are remarkably well supplied 

 with fishes and invertebrates. The advantages 

 this locality affords for biological research are 

 well known, as many naturalists have from 

 time to time resorted thereto for the study of 

 special problems. 



In the early fall Beaufort will be made the 

 headquarters of the steamer Fish-Hawk during 

 a biological and topographical survey of the 

 oyster grounds of the State which the Commis- 

 sion will conduct at the request of Professor J. 

 A. Holmes, director of the North Carolina 

 Natural History and Geological Survey, and 

 other State officials. 



Hugh M. Smith. 



U. S. Commission of 

 Fish and Fisheries. 



THEORY OF THE STEAM ENGINE. 



M. Nadal, in a very extended review of the 

 recognized ' Principles of the Mathematical 

 Theory of the Steam Engine,' in recent issues 

 of the Revue de Mecanique, discusses the theory 

 of heat-exchanges between working fluid and 

 cylinder-walls, the influence of the duration of 

 the admission period, that of the compression 

 and of the velocity of operation of the motor ; 

 touching upon the experimental work of Dwel- 

 shauvers-Dery. His principal conclusions are 

 the following : * 



1. The absorptive power of the metal in 

 contact with the vapor is finite, and variable as 

 a function of time. It is more considerable 

 than the emissive power. The variation of 

 this absorbing power is a function of the 

 amount of liquid deposited upon the wall, and 

 that amount has been shown by Donkin to 

 vary, in the cases reported by him, from 20 cal- 

 ories per square meter per unit difference of 

 temperature between metal and vapor, per sec- 

 ond, and, at the time of admission, down to 12 

 during expansion and lower, and to 2 during 

 the period of re evaporation and of emission, 

 and to even less values as exhaust becomes 

 complete ; although this re-evaporation may be 



* Revue de Mecanique, 1898-9. 



exceedingly rapid at the moment of opening 

 the eduction port. 



2. In the case of the unjacketed cylinder 

 the mean temperature of the wall is equal or 

 superior to that of the vapor in contact with it. 



3. The heat surrendered by the vapor at in- 

 duction increases less rapidly than does the 

 period of action, that of induction. The indi- 

 cations are that the range of temperature dur- 

 ing expansion mainly affects the quantity of the 

 heat-exchange and that the total temperature- 

 range does not measure the waste, which is 

 contrary to general opinion among engineers 

 and physicists. 



4. Compression in the clearance or ' dead 

 spaces ' is not always advantageous. 



M. Nadal shows that the moisture on the 

 wall plays an important part, augmenting the 

 quantity of heat- waste as superheating dimin- 

 ishes it. It is found that the variation of the 

 magnitude of heat-exchanges during the for- 

 ward and the return stroke accounts largely for 

 the well-established, and often large, gains due 

 to the use of the steam-jacket ; since that acces- 

 sory may communicate heat rapidly and effect- 

 ively during the earlier portion of the cycle, 

 while the sluggish transfer of heat out of the 

 cylinder wall during the period of low pressure 

 and temperature checks the wastes that would 

 otherwise then occur, and more extensively 

 than in the earlier period. Thus this variation 

 of transferring power of the wall acts as a sort 

 of ' check-valve ' for the heat received from the 

 jacket, permitting it to act efficiently, where 

 most needed and preventing loss of heat where 

 its transfer could do no good and would be 

 purely a waste. Thus the jacket, also, is most 

 economical in those engines which would be 

 most economical without it, those in which the 

 interior walls of the cylinder are dry during 

 exhaust. 



R. H. Thurston. 



THE PHILADELPHIA EXPOSITION OF 1900. 



We have received from the officers of the 

 Philadelphia Exposition of 1900 details in re- 

 gard to their plans. It is their purpose to ex- 

 hibit every kind of manufactured products of 

 the United States especially suitable for export. 

 Such exhibits will form the principal depart- 



