ASSOCIATIONS FOE THE ADVANCEMENT OF SCIENCE. (AMERICAN.) 



25 



sity, and with Agassiz, Gray, Levering, and others 

 did much toward inaugurating the great develop- 

 ment in science that took place in Harvard subse- 

 quent to the arrival of Agassiz in this country. He 

 chose as the subject of his address " Some Po'ints in 

 Theoretical Chemistry." He said : " All chemists 

 are familiar with the terms atom and molecule. 

 The use of these two words, with a clear conception 

 of their meaning, forms an era in the history of the 

 science. Our modern chemistry is built up of 

 atoms and molecules, as we now define them. Our 

 modern physics deals for the most part, and, as I 

 think, too exclusively, with atoms, except, perhaps, 

 in the case of what we now term physical chemistry, 

 the new branch of science, which makes it difficult 

 for us to determine where chemistry leaves off and 

 where physics begins. The old controversy between 

 the advocates of the continuity and those of the 

 discontinuity of matter is not dead, but only sleeps." 



Continuing, he added : " We owe to Dalton the 

 first clear conception of the chemical atom as dis- 

 tinguished from the atoms of Lucretius and De- 

 mocritus ; to Frankland the conception of valence, 

 which shows us what combinations of atoms can 

 exist consistently with the number of units of affin- 

 ity possessed by each individual atom, or, in other 

 words, in what manner groups of atoms can form 

 systems which are in stable equilibrium. This con- 

 ception includes that of the chemistry of space, now 

 so much employed in organic chemistry, as well as 

 that of the motions of atoms within the molecule, 

 as yet without supporters. To the conception of a 

 definite number of units of affinity recent chemistry 

 has added that of direction of action, statical ac- 

 cording to one school of chemists, dynamical accord- 

 ing to another. Within a comparatively short time 

 attention has been directed to a large class of com- 

 pounds exhibiting very interesting properties and 

 t'orming peculiar series, some of which, at least, are 

 made up of homologous terms. This group has been 

 called complex-inorganic, because many of its mem- 

 liers form highly complex molecules, of which no 

 analogues are known." 



He himself was one of the pioneer workers in 

 certain of these complex-inorganic acids and their 

 r>alts, and the history of his investigations formed 

 the burden of his address. He called attention to 

 the fact that " the term ' complex-inorganic ' was 

 at first intended to embrace all the compounds con- 

 taining a relatively large number of molecules of 

 tungstic and molybdic oxides as determinates, be- 

 ginning with the silicotungstates of Marignac. Hit- 

 tprf, in 1859, appears to have first drawn the dis- 

 tinction between double salts which are decom- 

 posed by solution and those which are stable under 

 the same circumstances. Finally, Ostwald proposed 

 to restrict the term ' complex ' to the salts which 

 are not decomposed by solution and which gave 

 none of the chemical reactions of the constituents. 

 Of these two classes it is difficult to say which is 

 the more interesting and theoretically important. 

 The salts of the first class are comparatively new 

 to chemists and, in spite of all which has' been 

 done, offer a very wide field for investigation. 

 Those of the second class present new species of 

 double and even of triple and quadruple salts. It 

 will first be necessary to study the whole subject 

 by physical as well as by the purely chemical meth- 

 ods which all chemists have hitherto employed, so 

 as to define as distinctly as possible the limit, if 

 there be one, which separates the two classes from 

 each other." 



In continuation he said : ;< I venture now to sug- 

 gest that, in addition to its valence, each atom and 

 each molecule possesses a special chemical potential, 

 not necessarily a function of its valence. The ex- 

 pression 'chemical potential 'is not wholly new. but 



I think the conception has never been clearly de- 

 fined. I would now define it as bearing the same 

 relation to chemical action which the electric po- 

 tential bears to electrical action, the two potentials 

 being mutually convertible, all chemical compounds 

 having residual affinities or potentials besides the 

 valencies. If we suppose that the atoms within the 

 molecule are in motion, such motion will be inde- 



Eendent of the valencies and the molecule will 

 ave a certain amount of free kinetic energy con- 

 vertible into chemical electrical energy or into 

 heat. In inorganic chemistry four great problems 

 now present themselves for solution. These are : 

 The existence and chemical relations of the gaseous 

 elements, of which five are known to exist in the 

 atmosphere ; the separation of the elements form- 

 ing the rare earths by systematic processes and the 

 determination of their positions in the periodic 

 series; the thorough and, so far as possible, ex- 

 haustive study of the complex and double salts; 

 and, finally, the determination of the atomic masses 

 of the elements with all the precision of which the 

 subject admits, and in the spirit of Stas, of Richards, 

 and of Morley." 



Proceedings of the Sections. The association 

 is divided into nine sections, each of which is pre- 

 sided .over by an officer having the rank of vice- 

 president of the association. Subsequent to the 

 opening proceedings each section meets by itself 

 and effects its organization by electing a fellow to 

 represent it in the council, a sectional committee of 

 three fellows, a fellow or member to the nominat- 

 ing committee, and a committee of three members 

 or fellows to nominate officers of the section for 

 the next meeting. As soon as this organization is 

 effected, the secretary of the section reports to the 

 general secretary, who then provides him with a 

 list of papers that, having been considered suitable 

 by the council, may be read and discussed before 

 the section. A press secretary, whose duties are to 

 prepare abstracts of the papers read and to give 

 them to reporters of newspapers, is also commonly 

 chosen. 



A. Mathematics and Astronomy. This section 

 was presided over by Dr. Edward E. Barnard, for- 

 merly at the Lick Observatory, and now at the 

 Yerkes Observatory, of the University of Chicago, 

 but perhaps best known by his discovery of the 

 fifth satellite of Jupiter. He chose as the subject 

 of his address "The Development of Astronomical 

 Photography." 



He said : The great discovery of taking pictures 

 by the natural light of the sun had just been made 

 when the American Association held its first meet- 

 ing, and while it then aroused great interest, there 

 yet were few who even dreamed of the future value 

 of photography to the world. One of those who 

 saw the value of Daguerre's discovery was the cele- 

 brated astronomer and writer Dr. Dick. The astute 

 Scotchman saw the opportunity to catch the fea- 

 tures of the moon by means of the photograph ; he 

 thought that the planets would prove easy subjects 

 to the new process, that perhaps there might be 

 something discovered about the nebuhe, and that 

 objects not visible to the eye might find themselves 

 depicted on the plated disks of Daguerre. It is a 

 little curious to note that while much excellent 

 work has been done on the nebula?, the photography 

 of the planets seems to-day no nearer realization 

 than in the days of Dr. Dick's predictions. In 

 1839 the astronomer Arago addressed the French 

 Academy on the subject of photographing the 

 skies, and within a year from that time the elder 

 Draper in New York had succeeded in taking a pic- 

 ture of the moon. Five years later, Harvard Col- 

 lege Observatory began its photographic work, 

 when were secured pictures of the moon with the 



