€ 
Grote,] 134 [June 16, 
the centrifugal force of rotation. The direct and reciprocal centres of 
linear oscillation, at 3 7and 47, tend to throw the node at $7 from or to- 
ward the centre. The reciprocal centre, 4 1, is pivotal in respect to the 
direct centre, 2 J, thus producing a secondary centre of linear oscillation 
at £/. This indicates the relative vis wiwa of radial projection which cor- 
responds to an oscillatory tangential vis viva of 1. The corresponding rela- 
tive velocity is 1/%. 
410. Propagation of Haplosive Waves. 
3erthelot and Vieille (Ann. de Chim. et de Phys., xxviii, 293) give the 
equation 0, = 0, ye na ue in which ( is the amount of heat set free at the 
q 
moment of chemical combination ; q, 278 times the specific heat ; @,, the 
velocity of explosive translation of gaseous molecules; @,, the velocity of 
mean translation after the explosive wave has ceased to exert any influence. 
They have verified the formula approximately, for a score of gaseous 
mixtures of very various compositions. They think that in the act of ex- 
plosion a certain number of molecules are thrown forward with all the 
velocity corresponding to the maximum temperature developed by the 
chemical combination ; this movement is transmitted from one inflamed 
edge to another, in a wave which is propagated with a velocity either 
identical, or comparable, to that of the molecules themselves, 
Introduction to a Study of the North American Noctuidae. By A. R. 
Grote, A. M. 
(Read before the American Philosophical Society, June 16, 1883.) 
In my ‘‘List of the Noctuide,’’ 1874, the ‘Check Lists ’’ of 1876 and 
1882, my ‘‘TIllustrated Essay ’’ and a number of different papers, I have 
explained the characters of Noctwidw, a family of moths of nocturnal 
habit and of very general distribution. These structural features, which 
are used in establishing genera and other divisions are briefly summarized 
as follows, taking the three divisions of the body in turn: 
I, The Head: character and structure of the compound eyes, which are 
either full or ovate, small, large, or more or less constricted, and have their 
surface naked or studded with hair, and the orbits sometimes provided with 
longer hair, dependent over the eye and called lashes ; the character and 
structure of the clypeus or front, between the eyes, which is swollen or 
flat and sometimes provided with a tubercle, or horns of various shapes 
and sizes, or a depression ; the presence of ocelli ; the shape and size of palpi 
and tongue ; the vestiture of the different parts, 
