July 30, 1915] 



SCIENCE 



163 



rior be encouraged. No new metliods are sug- 

 gested for securing these desirable ends, but 

 an excellent statement is made of reasons why 

 they should be sought. 



Chapter VI. was originally written as a pro- 

 test against eugenics of the more rabid sort, 

 and even in its present somewhat modified 

 form presents a rather strong contrast to the 

 preceding chapter. It takes issue with the 

 fatalistic, mechanistic, view of development, 

 which would assign to heredity all the ills that 

 flesh is heir to, and would deprive the indi- 

 vidual of all ability to alter his career and 

 character or to deviate from the course which 

 fate had marked out for him in the constitu- 

 tion of his germ-plasm. This protest had at 

 the time and still has occasion and utility. 

 The book as a whole is an attempt to evaluate 

 biologically heredity and environment, to show 

 that both are indispensable, and accordingly 

 that neither should be emphasized to the 

 neglect of the other. In this balanced view of 

 the two sets of agencies lies the peculiar merit 

 of this excellent book. 



W. E. Castle 



SPECIAL ABTICLES 



MAGNETIZATION BY ROTATION 



About six years ago I published in this jour- 

 nal a note in which it was shown that on the 

 modern theory of magnetism any magnetic 

 substance should become magnetized by a sort 

 of molecular gyroscopic process on being set 

 into rotation. Rotation should produce in any 

 substance an intrinsic magnetic intensity 

 parallel to the axis of rotation, proportional to 

 the angular velocity, and (like the magnetiza- 

 tion of the earth) directed oppositely to the 

 magnetic intensity which would be produced 

 by an electric current circulating around the 

 substance in the direction of rotation. If the 

 rotating body is magnetic, magnetization, pro- 

 portional to the intensity, should result ; other- 

 wise not (except to a very minute extent). 



Preliminary experiments mentioned in the 

 note referred to appeared, though doubtfully, 

 to show the effect in question in the case of a 

 large iron rod rotated at a speed of about 90 

 revolutions per second. Later observations 



made in much the same way, but with an at- 

 tempt at improvement in apparatus, failed to 

 confirm this result with any certainty; and 

 further investigation was postponed until 

 better facilities were available. 



Recently I have made, again with Mrs. 

 Barnett's assistance, experiments which have 

 yielded definite and conclusive results. In the 

 final experiments two nearly similar rods of 

 steel shafting were mounted with their axes 

 horizontal and perpendicular to the magnetic 

 meridian, and two similar coils of insulated 

 wire were mounted about their centers. These 

 coils were connected in series with one another 

 and with a Grassot fluxmeter, and were oppo- 

 sitely wound so that any variations in the in- 

 tensity of the earth's field produced no effect on 

 the fluxmeter. One of the rods remained at rest; 

 while the other, mounted in a region in which 

 the earth's magnetic intensity was compensated 

 by an electric current flowing in a very large 

 coil, was alternately rotated by an air motor 

 and brought to rest, the change of flux for 

 difl^erent speeds and different directions of ro- 

 tation being determined by the fluxmeter. 

 The fluxmeter was compensated for extraneous 

 electromotive forces, and was read by mirror 

 and scale to 0.1 mm. at the scale distance 8 

 meters. After all suspected sources of syste- 

 matic error were eliminated, an effect was 

 left corresponding precisely with that pre- 

 dicted by the above theory and inexplic- 

 able on any other theory hitherto proposed. 

 The intrinsic magnetic intensity of rota- 

 tion per unit speed, and the change of flux- 

 density at the center of the iron rod per unit 

 speed, were found to be 3.1 X 10"' gauss/r.p.s. 

 and 1.9 X 10"^ maxwells/cm.^ per r.p.s., re- 

 spectively. 



From experiments made for a difi'erent pur- 

 pose by Lebedew in 1912 it can be shown that 

 in non-magnetic substances not more than a 

 minute fraction of the magnetization we have 

 observed in iron is produced at the same speed. 



It is not, of course, possible to obtain iron 

 rods entirely free from magnetization, and ob- 

 servations were always made on changes of 

 residual flux. Together with the change of 

 flux proportional to the angular velocity, the 



