August 21, 1885.] 



SCIENCE. 



151 



siderable portion of time is given to certain 

 branches of mechanical engineering ; so that, 

 by his work in tlie laboratory of mechanical 

 engineering, the student becomes familiar with 

 the theory and practice of the steam-engine 

 and other motors, and acquires skill in the 

 use of the indicator and the different forms of 

 (i3'namometer, and also takes part in numerous 

 boiler and engine tests. He thus gains a knowl- 

 edge, which, in case he enters upon any appli- 

 cation of ch'uamo-electric machinery, will be 

 very important to him. 



Throughout the last 3'ear an extended course 

 of lectures is given upon the technical applica- 

 tions of electricity, in which the theory and 

 practice of telegraphj', both land and sub- 

 marine, telephony, electric lighting, and the 

 electrical transmission of power, are discussed. 

 In order to add to the value of this course, 

 the lectures and laboratorj^ exercises given by 

 the regular teachers of the school are supple- 

 mented by instruction from various gentlemen 

 who are professionally^ engaged in the practi- 

 cal development of electrical science, who give 

 courses of lectures, or single lectures, upon 

 special subjects ; so that the student has the 

 opportunit}' of learning exactly what is con- 

 sidered as good practice among those actually 

 employed in the profession which he has 

 chosen. 



In an}' course of this nature, very much 

 depends upon the facilities which are furnished 

 in the way of instruments for precise measure- 

 ment. The importance of a proper supply of 

 such apparatus has been recognized ; and the 

 Rogers laboratory of physics, in which the ex- 

 perimental electrical work is carried on, is well 

 supplied with the necessary facilities. For 

 line-testing, the student has access to actual 

 telegraph-lines, and learns the methods of 

 working most suitable for such purposes. Also 

 an experimental study is made of dynamo- 

 electric machinerj', electrical motors, electric 

 illuminating apparatus, and other similar appli- 

 ances . The student is further required to u nder- 

 take a certain amount of work of an original 

 nature, and is thus stimulated to enter upon 

 scientific research. A well-selected reference 

 library, containing most of the physical and 

 electrical journals, together with the leading 

 works on these subjects, is accessible at all 

 times. 



The aim of the course, as a whole, is to give 

 an education in which theory and practice shall 

 go hand in hand. The pupil is taught, that, as 

 science advances, the two become more and 

 more closely allied ; so that his professional 

 success will be most probable, if, to as thorough 



a knowlege of theory as he can acquire in the 

 four years of his undergraduate study, he adds 

 a large amount of practice in the application 

 of his theoretical knowledge to the solution of 

 the problems with which the electrical engineers 

 of the present time are especiall}' concerned. 

 And an attempt, at least, is made to give him 

 such a preliminar}^ training, that he will find 

 himself well furnished with the necessary knowl- 

 edge to continue his studies bj^ himself, as 

 opportunit}' may afterwards be furnished, or 

 occasion require. 



ELECTRICAL MEASURING INSTRU- 

 MENTS. 



For the quantitative determination of an electrical 

 current, any one of its effects may be employed, the 

 law of which is known ; and the choice of the effect 

 to be utilized in the construction of a measuring 

 instrument will be influenced by different considera- 

 tions in different cases. The requirements of the 

 practical uses of electricity necessitate, in general, 

 instruments capable of measuring currents of great 

 strength, varying through a wide range. The instru- 

 ments must unite the characteristics of compactness 

 and portability with simplicity of mechanism and 

 manipulation, thus excluding many of the methods 

 available in the permanent physical laboratory. The 

 devices which have been employed are so various, 

 and the forms of apparatus so manifold, that a mere 

 catalogue of them would reach beyond the proper 

 limits of an article. As they naturally fall into a 

 comparatively small number of groups, however, the 

 leading characters of certain typical forms may he 

 indicated within a moderate compass, and the merits 

 or defects of some of the more prominent pointed 

 out. 



The most common and obvious method of meas- 

 uring an electrical current depends upon the deflec- 

 tion of a magnetic needle by the current itself. The 

 simplest arrangement would be to use a straight 

 vertical wire situated in the meridian of a very short 

 magnetic needle, and at a moderate distance from it. 

 Within certain limits of approximation, the tangent 

 of the angle of deflection is proportional to the cur- 

 rent strength. If the distance of the needle from 

 the wire is made variable, an empirical scale can be 

 experimentally formed, from which, in subsequent 

 use, the current strength may at once be known from 

 a single observation of deflection, the horizontal 

 component of the earth's magnetism being supposed 

 invariable, or its variation determined and allowed 

 for in the reduction. In a permanent installation, 

 such a plan would be feasible, and capable of giving 

 useful results. But it involves some practical difficul- 

 ties, the most prominent of which are the consider- 

 able lengtli which must be given to the wire, and the 

 fact that the wires bringing the current to the vertical 

 portion of the circuit would themselves produce a 

 disturbing effect upon the needle, unless particular 



