97 



Dr. Coates stated that the result of a number of examinations, made 

 in the vicinity of Philadelphia by several observers, on the crops of 

 the present year, has proved the pale yellow larva in the hollow of 

 the straw of wheat, to be the same with that which is ultimately con- 

 verted into the Cecidomyia Destructor of Say, and the Hessian Fly 

 of our cultivators. In many instances, referrible perhaps to a pecu- 

 liarity in the present season, the animal went through all its stages 

 before escaping from the cavity; thus affording irrefragable evidence 

 of the identity of the species. 



In no case known to Dr. C. had any thing resembling a caterpillar 

 or maggot, or any thing apparently capable of locomotion, been found 

 under the sheath of the leaf: the body observed, was always immo- 

 vable, and fixed in a depression of the straw. 



Nor was any insect known to have been found which approached 

 to the genus Lasioptera, as given by Meigen ; all those examined in 

 the perfect state, which were not the Ceraphron, since referred to 

 Pteromalus and Eurytoma, in either its four-winged or its apterous 

 form, being tipulide animals, and betraying no important difference 

 from those observed by Mr. Say. 



Dr. C. called attention to several notices of this subject in the Pro- 

 ceedings of the Academy of Natural Sciences. 



Professor Henry, of Princeton, exhibited to the Society a 

 simple form of the Heliostat, or instrument for throwing a sta- 

 tionary beam of light into a darkened room. 



He stated that this article of apparatus, which is indispensable in 

 delicate experiments on light, is in its usual form a very complex in- 

 strument, and consequently very expensive; while the one to which 

 the attention of the Society was directed, is very simple, and scarcely 

 cost more than the tenth part of the price of one of the old form. 



It was made in accordance with the plan given by Dr. Thomas 

 Young in the first volume of his Lectures on Natural Philosophy, 

 which consists in reflecting a beam of light into the room in a line 

 parallel to the axis of the earth, and then causing it to retain this 

 direction by giving the reflector a rotatory motion equal to the appa- 

 rent motion of the sun. The instrument consists of a flat block of 

 mahogany, about nine inches long and five inches wide, on which is 

 placed, in an inclined position, the wheel work of a common pocket 

 watch. This serves to give rotatory motion to a brass wheel of about 



