August 19, 1921] 



SCIENCE 



155 



in his " Introduction to Historical Geology " 

 (1916), says (p. 232) : 



Insects such as bees, ants and wasps made their 

 first appearance in the Jurassic. 



Dr. C. Schuchert, in " Historical Geology " 

 (" Text-book of Geology," part 2), 1915, p. 812, 

 states that " with the Comanchian . . . insects 

 (beetles, flies, ants, bees, wasps) took their rise." 

 As a matter of fact, the oldest known bees are 

 from Baltic amber (Oligocene Tertiary), and 

 the oldest known true wasps and ants are from 

 the Eocene. In the Jurassic, the peculiar 

 family Pseudosiricidse, apparently related to 

 the modern Sirieidse, were well represented. 

 One species of this extinct family (Megapte- 

 rites mirahilis Ckll.) has lately been described 

 from the English Eocene. There is a very 

 dubious Jurassic Hymenopterous insect from 

 Spain, supposed to be related to the Ichneu- 

 monidse. These Hymenoptera were not in any 

 way adapted to be pollinators of flowers. Con- 

 sidering the development of the Hymenoptera 

 in the Eocene, it may be presumed that the 

 wasps and ants, at least, originated as early as 

 the Cretaceous, but there is no direct evidence 

 on the poin<t. 



T. D. A. COCKERELL 



UNr?ERSiTT OP Colorado 



SPECIAL ARTICLES 



THE PNEUMATIC PARADOX IN ACOUSTICS 



1. The following pretty experiment is very 

 instructive in its bearing on the Mayer- 

 Dvorak effect, as well as on the experiments 

 of the present paper. In the figure, 6 is the 

 light wooden beam (30 cm. long, counter- 

 poised at a) of a horizontal torsion balance, 

 the torsion wire (of brass, .02 cm. in diameter 

 and 18 cm. long on either side normal to the 

 diagram) being seen at w. A light disc of 

 cardboard d is suspended in equilibrium from 

 the end of the balance. Below this is the 

 telephone T to which the brass pipe p (13 cm. 

 in length and 2.6 cm. in diameter) has been 

 cemented, to form of a closed c" organ pipe 

 of which the telephone plate is the bottom. 

 The open top of p is surrounded by a fixed 

 annular disc cc of metal parallel and close 

 to the movable disc d. 



When the telephone is strongly energized 

 and emits a rising note (motor break and rheo- 

 stat), no effect is produced until its frequency 

 is in resonance with the pipe p, whereupon the 

 disc d is at once attracted. Since the pipe p 

 is closed above by this process, the telephone 

 frequency must be slightly reduced to keep 

 the discs in cohesion. On breaking the cur- 

 rent d is at once released. 





^ 



d 



e r 



This is of course nothing further than a 

 modified example of the familiar pneumatic 

 paradox. When the pipe howls, the distance 

 from which d may be attracted and held is 

 perhaps 2 cm. beyond which the couche of 

 diminished static pressure is ineffective. The 

 thickness vanishes with the intensity of sound. 



2. If now cc is removed and the disc d is 

 replaced by the closed paper cylinder e of a 

 diameter (2.1 cm.) sufficiently small to enter 

 the mouth of p easily, the results of the ex- 

 periment are the same. Here however the 

 cylinder e may be made to enter the pipe as 

 much as 1 cm. or more by successively decreas- 

 ing the pitch, conformably by the gradually 

 stopped mouth of p. Supposing the total dis- 

 placement to be 2 cm., the force indicated by 

 the torsion balance would be .7 dyne and the 

 mean pressure decrement for the area 3.5 

 cm.-, therefore .2 dynes/cm.- But as both the 

 disc and cylinder come down with a jerk, the 

 maximum forces are probably larger. 



If there were a pin hole in the bottom of Bj 



