May 23, 1913] 



SCIENCE 



803 



timber, such, for instance, as making alcohol 

 from wood waste; in addition. Products is 

 gathering much statistical information of use 

 not only to the Forest Service, but to all 

 wood-using industries. Products comes in 

 closer contact with the lumber industry than 

 any other branch of the service and has al- 

 ready secured results of great value to lum- 

 bermen. Under Silviculture, the Review 

 gives in some detaO. the important problems 

 on which the service is working. It describes 

 briefly the establishment and purpose of the 

 experiment stations; under each head (for- 

 estation, forest influences, management, etc.) 

 it not only gives the problems to be studied, 

 but shows their importance and their relation 

 to each other. The experiment being con- 

 ducted at Wagon Wheel Gap to determine the 

 influence of forest cover on run off and ero- 

 sion is given rather fully. This is probably 

 the most complete and far-reaching experi- 

 ment of its kind in the world. 



At the end of the Review is the investiga- 

 tive program for 1912. A study of this pro- 

 gram will show the thoroughness with which 

 the field is being covered. 



Baerington Moore 



Washington, D. C. 



SPECIAL ASTICLES 

 a laboratory method of demonstrating the 

 earth's rotation 

 The two laboratory methods in general use 

 for proving the rotation of the earth are 

 Poucault's pendulum and gyroscope experi- 

 ments. The first is inapplicable in many 

 laboratories, becausa there is no convenient 

 place to hang a sufficiently long and heavy 

 pendulum, while the apparatus for the second 

 is necessarily expensive. The following ex- 

 periment is designed to provide a simple and 

 convenient means by which the earth's rota- 

 tion may be demonstrated in a small labora- 

 tory. The demonstration depends upon the 

 fact that, if a circular tube filled with water 

 is placed in a plane perpendicular to the 

 earth's axis, the upper part of the tube with 

 the water in it is moving toward the east with 

 respect to the lower part. If the tube is 



quickly rotated through 180 degrees about its 

 east and west diameter as an axis, the part of 

 the tube which was on the upper side attains 

 a relatively westward motion as it is turned 

 downwards (since it is drawing nearer the 

 earth's axis). But the water in this part of 

 the tube retains a large part of its original 

 eastward motion, and this can be detected by 

 suitable means. 



Since the east and west axis itself is ro- 

 tating with the earth, only that component of 

 the water's momentum which is parallel to 

 this axis will have an effect in producing a 

 relative motion when the tube is turned. If 

 then a is the angular velocity of the earth's 

 rotation, r the radius of the circle into which 

 the tube is bent, and 6 the angular distance 

 of any small portion of the tube from the east 

 and west axis, the relative velocity between 

 the water and the tube when it is quickly 

 turned from a position perpendicular to the 

 earth's axis through 180 degrees is 



Velocity = V - 



— I SIE 



In order to prevent convection currents, it 

 is best to hold the ring normally in a hori- 

 zontal position, in which case the relative 

 motion is of course ar sin <f,, where <^ is the 

 latitude of the experimenter. 



To perform the experiment, glass tubing 

 1.3 cm. inside diameter was bent into a cir- 

 cular ring 99.3 cm. in radius, and a short 

 glass tube closed with a rubber tube and screw 



clamp was sealed into it to allow for the ex- 

 pansion of the water and to provide a place 

 for filling. The ring was fastened with tape 

 into notches in the wooden rod A (Fig. 1), 

 which served as the horizontal axis, and was 



