232 



SCIENCE. 



[Vol. IT., No. 84. 



nicated during the hour to which the exercise is 

 confined, when the number of students in the recita- 

 tion-room is thirty, forty, or even fifty? What a 

 perversion of the purposes of the noble endowments 

 for higher education, to expend almost the entire 

 energy of the teaching force of the many institutions 

 which adopt this system, in a daily effort to weigh with 

 minutest accuracy the fidelity with which assigned 

 tasks have been committed to memory! The most 

 diverse views may be entertained as to whether the 

 college course can embrace analytical mechanics, or 

 the theory of determinants (now so universally used), 

 or whether it can omit vector and quaternion anal- 

 ysis. When, however, it is known that in a small 

 western college graduating less than a dozen annu- 

 ally, we have now had for years volunteer classes, 

 pursuing all these and other subjects annually, with 

 success, the possibility of including them in a college 

 curriculum must be acknowledged. 



In conclusion, Professor Eddy wished to call for 

 reform in our mathematical teaching. Let it not be 

 so conducted that he who has neither taste for the 

 study, nor special knowledge of it, stands on an equal 

 footing as a teacher with the man of real mathemati- 

 cal insight. Now is a favorable time for revising our 

 estimates of what can and ought to be done in this 

 field. Higher mathematical culture has commenced 

 a new and fruitful growth in this country in various 

 places; and an association of the mathematicians of 

 this country might be of service for the purpose of 

 concerted action in improving the mathematical train- 

 ins; in our colleges. 



WHAT IS ELECTRICITY? 1 



All Professor Trowbridge hoped to do was to make 

 his audience ask themselves the question with more 

 humility and a greater consciousness of ignorance. 

 We shall probably never know what electricity is, any 

 more than we shall know what energy is. What 

 we shall be able, probably, to discover, is the rela- 

 tionship between electricity, magnetism, light, heat, 

 gravitation, and the attracting force which manifests 

 itself in chemical changes. Fifty years ago scientific 

 men attached a force to every phenomenon of nature : 

 thus there were the forces of electricity and magnet- 

 ism, the vital forces, and the chemical forces. Now 

 we have become so far unitarian in our scientific 

 views, that we accept treatises on mechanics which 

 have the one word 'Dynamik' for a title; and we 

 look for a treatise on physics which shall be entitled 

 ' Mechanical philosophy,' in which all the phenomena 

 of radiant energy, together with the phenomena of 

 energy which we entitle electricity and magnetism, 

 shall be discussed from the point of view of mechan- 

 ics. What we are to have in the future is a treatise 

 which will show the mechanical relation of gravita- 

 tion, of so-called chemical attracting force, and elec- 



1 Abstract of an address before the section of physics of the 

 American association for the advancement of science, at Phil- 

 adelphia, Sept. 4, by Prof. John Trowbridge of Harvard col- 

 lege, Cambridge, vice-president of the section. 



trical attracting force, and the manifestations of ^hat 

 we call radiant energy. We have reduced our knowl- 

 edge of electricity and magnetism to what may be 

 called a mechanical system, so that in a large number 

 of cases we can calculate beforehand what will take 

 place, and we are under no necessity of trying actual 

 experiments. It is probable, for instance, that the 

 correct form of a dynamo-machine for providing the 

 electric light can be calculated and the plans drawn 

 with as much certainty as the diagrams of a steam- 

 engine are constructed. We may congratulate our- 

 selves, therefore, in having a large amount of system- 

 atic knowledge in electricity: and we see clearly how 

 to increase this systematic knowledge; for we have 

 discovered that a man cannot expect to master the 

 subject of electricity who has not made himself famil 

 iar with thermo-dynamics, with analytical mechanics, 

 and with all the topics now embraced under the com- 

 prehensive title of 'physics.' 



Out of all the theories of electricity, the two-fluid 

 theories, the one-fluid or Franklin theory, and the 

 various molecular theories, not one remains to-day 

 under the guidance of which we are ready to march 

 onward. We have discovered that we cannot speak 

 of the velocity of electricity. All that we can truly 

 say is, we have a healthy distrust of our theories, and 

 an abiding faith in the doctrine of the conservation 

 of energy. 



It is one thing to become familiar with all the ap- 

 plications of the mechanical theory of electricity, and 

 another to make an advance in the subject so that we 

 can see the relations of electrical and magnetic at- 

 traction to the attraction of gravitation and to what 

 we call chemical attraction. To this possible relation- 

 ship, Professor Trowbridge wished to call attention. 

 The new advances in our knowledge of electrical 

 manifestations are to come from the true conception 

 of the universality of electrical manifestations, and 

 from the advance in the study of molecular physics. 

 When we let an acid fall from the surface of a metal, 

 the metal takes one state of electrification and the 

 drop of acid the other: in other words, we produce a 

 difference of electrical potential. On the other hand, 

 a difference of electrical potential modifies the aggrega- 

 tion of molecules. The experiments of Lippman are 

 well known. He has constructed an electrometer and 

 even a dynamo-electric machine which depend upon 

 the principle that the superficial energy of a surface 

 of mercury covered with acidulated water is modified 

 when a difference of electrical potential is produced 

 at the limiting surfaces. The manifestations of what 

 is called superficial energy, — that is, the energy mani- 

 fested at the surface of separation of any two sub- 

 stances, — and the effect of electricity upon the super- 

 ficial energy, afford much food for thought. There 

 have always been two parties in electricity, — one 

 which maintains that electricity is due to the contact 

 of dissimilar substances, and the other party which 

 believes that the source of electrical action must be 

 sought in chemical action. Thus, according to one 

 party, the action of an ordinary voltaic cell is due to 

 the contact, for instance, of zinc with copper; the acid 

 or solution of the cell merely acting as the connecting 



