186 On the Flow of Elastic Fluids through Orijicps, 



accurately measured from month to month. Two sucli pins in 

 the surface of an Astraea, would in the same manner, by the en- 

 larging distance between, show the rate of increase in the cir- 

 cumference of the hemisphere; or if four were placed so as to 

 enclose an area, and the number of polyps counted^ the numeri- 

 cal increase of polyps resulting from budding, might be ascer- 

 tained. It is to be hoped that some of the foreign residents at 

 the Sandwich, Society, Samoan or Feejee Islands will take this 

 subject in hand. There are also many parts of the West Indies, 

 where these investigations might be conv^enienlly made. 



The applications of the facts reviewed occupy us in our next 

 chapter. 



Art. XX. — On the Flow of Elastic Fluids through Orifices ; 

 with a suggestion of a new method of determining the mutual 

 relations of Elastic Force^ Temperature and Density in an 

 Expanding Fluid ; by Eli W. Blake. 



In volume v, Second Series, of this Journal, page 7S^ I proposed 

 a new theory of the flow of elastic fluids through orifices, differ- 

 ing essentially from that heretofore received. The chief object 

 of the present article is to give an account of an experiment in- 

 stitnted for the purpose of testing the truth of that theory. 



The fundamental points of difference between the old theory 

 and the new, are as follows : 



1. The old theory regards the constant force which expels the 

 fluid as being, in all cases, equal to the difljerence between the 

 elastic forces of the fluids in the two vessels. 



The new theory regards it as equal to that difference only 

 when the less exceeds half the greater; and in all other cases as 

 equal to half the greater. 



2. The old theory considers the fluid as passing the orifice with 

 a density equal to that in the discharging vessel. 



The new theory considers it as passing the orifice with a deri- 

 sity equal to that in the receiving vessel, whenever this last is 

 equal to or greater than half the density in the discharging ves- 

 sel ; and in all other cases, with half the density in the discharg- 

 ing vessel. 



The formula for the quantity discharged in a given time, pred- 

 icated upon the new theory, gives, in all cases, less than that 

 predicated upon ihe old theory. In the case of a flow into a 

 vacuum, the difference amounts toone half. 



The scheme devised to test the relative merits of the two 

 theories, was founded upon the following considerations, viz.: 

 When air rushes from the atmosphere into a receiver wholly or 

 partially exhausted, passing on its way through a small interme- 

 diate vessel or chamber, entering that chamber and passing out 



