Septembee 28, 1917] 



SCIENCE 



313 



the angle GIJ is somewhat less than 45°. The 

 center of gravity of the system then lies ver- 

 tically below the cord. Choose axes fixed in the 

 body as follows : For the axis 1 take a horizon- 

 tal line through the center of gravity and per- 

 pendicular to the plane GIJ, for axis 5 take 

 the axis of the rod, and for axis S take a line 



through the center of gravity and perpendicu- 

 lar to the plane of 1 and 2. 3 will then lie in 

 the plane GIJ. These axes are represented in 

 the figure, where the axis 1 is supposed to pro- 

 ject directly towards us, and the coordinate 

 system is consequently right handed. Take 

 right-handed rotation as positive. Then 

 Euler's first equation may be written 



(B — C)u:ai, = L, 



(1) 



where A, B, and C stand, respectively, for the 

 moments of inertia about the axes 1, 2, 3; w,, 

 (D„ <0j for the angular velocities about those 

 same axes; and L for any external torque 



which may be acting about axis 1. In the 

 present case we have very nearly B = and 

 0= A, so that equation (1) becomes 



_-fa,,u>,_-. 



(2) 



Now give to the system a right-handed rota- 

 tion about I J. We then have w, > and 

 W3 > 0. If the center of gravity were to stay 

 immediately below the cord we should have 

 L^O and therefore dwjdt < 0. But this 

 would increase the angle and so throw the 

 center of gravity out from underneath //. The 

 weight of the system and the tension in IJ 

 would then supply a positive torque L. It is 

 possible to have this torque of such magnitude 

 as to make diajdi = 0, in which case the torque 

 is entirely non-momental. The reason for the 

 necessity of this non-momental torque is easily 

 seen by considering an element of the rod near 

 G or H. When the rod is rotating there must 

 act upon this element a centripetal force di- 

 rected toward the axis IJ. This force is sup- 

 plied by means of the torque L. 



A rotation of svtfficient magnitude to make 6 

 very evidently greater than it is when the sys- 

 tem is at rest is easily imparted by hand. 



Arthur Taber Jones 



Smith College 



A UNIQUE HORNET'S NEST 



In the magazine. The Guide to Nature, Vol. 

 10, No. 1, June, 1917, Earl A. Newhall, of 

 Shelburne, Mass., under the title " The nest of 

 an unknown hornet," mentions a hornet's nest 

 of peculiar form which he found hanging un- 

 der the eaves of an old shop. An excellent 

 photograph of this strange nest accompanies 

 the article. ISTewhall wrote to Dr. L. O. 

 Howard, of the Bureau of Entomology, send- 

 ing a photograph of the nest. Dr. Howard 

 states : 



I never saw a hornet's nest like the one in the 

 photograph and I have referred your letter to Mr. 

 S. A. Eohwer, of this bureau, who has studied these 

 creatures for many years and he replies as fol- 

 lows: "I have never seen a nest like this before 

 and do not know if it is an abnormal one or not. 

 If possible, I should like to have some of the ma- 



