Chemistry and Physics. 125 



experimental test by Silvantjs P. Thompson and the results 

 obtained show that the hypothesis of a momentary paralysis of 

 the sense of vision is unnecessary. 



The sector disc making from two to six revolutions per second 

 presents a uniform gray tint. At the instant when the intermit-* 

 tence is produced, either by stamping the foot or tapping the 

 head, the most prominent effect observed by Thompson was the 

 enhanced brightness of stationary white sectors and not the 

 momentary appearance of stationary gray or black sectors. 

 " A momentary paralj'sis, if it occurred, should produce momen- 

 tary blackness of the entire disc, which is not what happens." 

 To subject the matter to further test, the author arranged a 

 revolving sector disc, driven at constant angular velocity by a 

 small electric motor, in such a manner that it could be observed 

 either directly from a distance of a few feet or by reflection in a 

 small plane mirror held in the hand or clamped elastically 

 between two rubber stoppers supported by a rigid stand. When 

 a slight mechanical shock was given to the mirror so as to alter 

 momentarily and by a small amount the apparent position of the 

 revolving disc, an intermittence was produced of the same kind 

 as was observed when a shock was given to the head or body. 

 The sectors appeared to stand still, and the brightness of the 

 white sectors was temporarily increased. " This intermittence, if 

 such it can be called, occurs equally whether the observer taps 

 the mirror or whether some other person taps it." "The pheno- 

 menon is in this case independent of any mechanical acceleration 

 of the nerves or nerve-structures, and is not due to any temporary 

 paralysis of vision." 



" The explanation appears to be that when the moving images 

 of the white sectors on the retina are suddenly shifted by a minute 

 displacement, they fall on some of the rods and cones which are 

 relatively unfatigued, and which, for the instant, are therefore of 

 greater sensitiveness." The writer of this notice desires to call 

 attention to the fact that the phenomenon in question can be 

 observed while walking heavily on the pavement and watching 

 the spokes of the wheels of passing automobiles. (Yellow wheels 

 can be seen better than red or black ones, of course.) — Proc. Roy. 

 Soc, vol. xc (A), p. 448. h. s. v. 



7. JBausteine zur Flugbahn- and Kreisel-Theorie ; \>y August 

 Dahne. Pp. 44, with 5 figures. Berlin, 1914 (R. Eisenschmidt). 

 — The text of this monograph is divided into two parts, the first 

 and second of which deal respectively with the theory of the 

 rotation of rigid bodies and the motion of projectiles. In the 

 first part the author attempts to show that some of the current 

 explanations of gyroscopic phenomena are incorrect. In particular 

 he criticizes adversely both Poinsot's theory of the composition of 

 simultaneous infinitesimal rotations and Poggendorff's elementary 

 explanation of the starting of precession. On page 17 Dahne 

 comes to the conclusion " that the deviation of a rotating body 

 must take place not only when an attempt is made to alter the 



