ALvRcn 15, 1918] 



SCIENCE 



271 



To those who studied their psychology with 

 the introspectionist school it must be strange 

 to find brought together under a psychological 

 heading, the work of the physiologist on drugs 

 and fatigue, of the engineer on motion-study, 

 of the biologist on heredity, of the psychiatrist 

 on mental abnormality, of the clinician on 

 mental development, and of the educator on 

 learning, in addition to the research of the 

 psychologists. It marks the change in psy- 

 chology to the more objective study of be- 

 havior. Applied psychology rejoices that it 

 affords a clearing house for any knowledge 

 which bears directly upon the understanding 

 and control of human action. 



The authors cite telling examples in which 

 scientific studies of the human factor have 

 produced better results than the hit-or-miss 

 methods of practical sense in dealing with busi- 

 ness, industrial, and professional problems. 

 In many other cases than industrial accidents 

 it will doubtless be found that the most im- 

 portant cause to be controlled is not in the 

 field of the applied physicist but in the field 

 of human engineering. In leaving the book, 

 if the reader still feels that we are yet only 

 on the threshold of a new pursuit, he will at 

 least liave foimd abundant evidence scientifi- 

 cally formulated to convince him that we are 

 on the threshold and not merely viewing the 

 house at a distance. J. B. Miner 



C.\RNEGiE Institute op Technoloot 



SPECIAL ARTICLES 



NOTE ON THREE DEVICES FOR USE IN 



ELECTROMETRY 



During recent work with an electrometer 

 the author has employed three devices which 

 are obvious enough and can hardly be novel, 

 but which seem worth putting more definitely 

 on record as tested devices. 



(1) A simple means of increasing the de- 

 flections of an electrometer is often wanted 

 under circumstances where the use of a suffi- 

 ciently long distance from mirror to scale is 

 inconvenient. This may be accomplished by 

 interposing a concave lens between mirror 

 and scale, thus magnifying the deflection. 

 A lens of rather long focus placed, if anytihug 



nearer the mirror (fig. 1) is preferable, as the 

 effects of chromatic aberration are thereby 

 diminished and the proportionality of the 

 deflections is also better preserved. The 

 image will be much brighter if a cylindrical 

 lens is used; such a lens can be secured 

 quickly and at small expense as a special 

 order from Bausch & Lomb. 



By this means a Dolezalek electrometer 

 with platinum fiber was raised from 3,000 to 

 18,000 mm. per volt at a scale distance of 

 4 m. Owing to diffraction, the spot was about 

 1 mm. wide, but its position could be read 

 to 0.2 mm., and the proportionality between 

 deflection and potential was very good. 



(2) Sometimes one wants a simple means 

 of connecting two wires together which will 

 permit of easier disconnection than a soldered 

 joint and yet will not introduce the additional 

 capacity and possible leakage of a key. For 

 this purpose one may solder a little silver 

 cup to one wire and then attach the other wire 

 to a piece of heavy wire tipped with a silver 

 point and bent so that the point rests upon 

 the floor of the cup (fig. 2). Silver oxide 

 being a fairly good conductor, the slight pres- 

 sure thus obtained is quite sufficient to make 

 good contact. 



(3) To obtain time signals at rather long 

 intervals a torsion pendulum is more useful 

 than a gravity pendulum because of the ease 

 with which the period may be varied over a 

 wide range. If the inertia system consists 

 of a light cross-rod carrying two heavy sliding 

 weights, then the period is approximately pro- 

 portional to the distance of the weights from 

 the center, so that a range of 1 to 10 in the 

 period is easily obtained. The system can be 



