422 Entomological Society. 



described an air Engine, invented by his brother and himself. The 

 movements are founded upon the well-known pneumatic principle, 

 that air has its bulk or pressure increased or diminished in proportion 

 as its temperature is raised or lowered. The application of this 

 principle was exemplified by drawings, and a model exhibiting a ma- 

 chine composed of two strong tight air vessels, connected with the 

 opposite ends of a vertical cylinder, in which a piston works in the 

 usual manner. Within these air vessels are suspended two air-tight 

 vessels, or plungers, filled with non-conducting substances, and at- 

 tached to the opposite extremities of a beam, capable of moving up 

 and down alternately, to the extent of one-fifth of the depth of the 

 air-vessels. By this motion of the plunger, the air which is in a 

 heated state below is moved to the upper part of the vessels, and in 

 its transit traverses a series of vertical capillary passages between 

 three metallic plates, which absorb the major part of the caloric. 

 The remainder is taken up by a refrigerator of tubes filled with 

 water. The air at the heated end is about 700 degrees, and has a 

 proportionate pressure ; when it arrives at the cooled end it is reduced 

 to about 150 degrees, and the pressure diminished to a correspond- 

 ing extent. Therefore, as the internal vessels move in opposite di- 

 rections, it necessarily follows that the pressure of the condensed air 

 in one vessel is increased, while that of the other is diminished. A dif- 

 ference of pressure is thus produced upon the opposite ends of the 

 piston, and a reciprocating motion results, which communicates 

 through a beam, connecting rod, crank, and fly-wheel to the ma- 

 chinery when driven. Machines on this principle were stated to 

 have been worked, for some years past, at Dundee, with considera- 

 ble saving of fuel, as compared to a steam-engine of similar power, 

 and doing the same work. It is now proposed to adapt it to marine 

 purposes, to which, from its simplicity and slight expenditure of fuel, 

 it appeared well fitted. — Athenaeum, June 21, 1845. 



Entomological Society. — June 2. — The Rev. F. W. Hope, Pre- 

 sident, in the chair. — Various new species of insects were exhibited, 

 including a fine species of Trictenotoma, from the Himalayas, by Capt. 

 Parry, the male of the rare and singular Dorthesia characias by Mr. 

 Weir, an apparently new Tortrix, by Mr. Douglas, and living 



