20 



SCIENCE. 



[N. S. Vol. XII, No. 288. 



tries makes for the advancement of science 

 and art. But time has changed this some- 

 what, and I think it will change it more. 



With regard to all the sciences a large 

 number of misstatements are made regard- 

 ing their commercial value. Probably As- 

 tronomy has been of as much benefit to 

 mankind as any. Every ocean passenger 

 owes to it his safe and rapid passage. 

 Through its help the carriage of every ton 

 of freight is made cheaper. It would be 

 difficult to calculate the money value it has 

 been to the world. 



The conception which most people have 

 of the nature of the questions to be solved 

 in Astronomy is a false one. They look on 

 them as text-book problems in mathematics 

 which are arranged to come out nicely. 

 They suppose such questions can be solved 

 definitely and exactly, once for all. They 

 do not know that instruments are imperfect 

 and that observers have personal errors, 

 nor that it is possible to be sure only to a 

 certain limit, personal opinion founded on 

 experience carrying us a little farther, and 

 the rest being uncertain, though methods 

 and instruments and mathematical concep- 

 tions may, after a while, be improved. So 

 that in any actual question in practical or 

 theoretical Astronomy it is necessary to 

 deal with facts as they are in nature, and 

 obtain the best possible solution, though 

 perhaps not the one which is exactly true. 



Many people, too, and well educated ones, 

 have very curious ideas as to the amount 

 of labor involved in the solution of ques- 

 tions in Astronomy, and as to the progress 

 of the science. An intelligent doctor, who 

 knows that the science of medicine, as far 

 as it is a science, is something of slow 

 growth, who experiments for a year or two 

 on some fairly simple question, cannot un- 

 derstand the same thing in Astronomy, and 

 thinks that it was really founded and de- 

 veloped by some one whom he happens to 

 know about. 



In the case of the small observatories, 

 where teaching is expected of the astron- 

 omer, the question of economy of time is a 

 difficult one. At Harvard and Johns Hop- 

 kins, for instance, six hours of lectures per 

 week would be expected to occupy half of 

 a teacher's time, while in a small establish- 

 ment one cannot give that proportion and 

 make and reduce observations. At the 

 smaller observatories, too, there is difficulty 

 in requiring proper preparation and in en- 

 forcing a high standard of scholarship. 

 Men who believe that the training in law, 

 medicine or engineering should be thorough 

 and severe, because they think the students 

 will be better off commercially, cannot un- 

 derstand that students in Astronomy ought 

 to have the same thorough discipline. 



THE EIGHTH GROUP OF THE PERIODIC SYS- 

 TEM AND SOME OF ITS PROBLEMS. 

 II. 

 We have seen that nearly half a century 

 ago, it was clear to Claus that iron, ruthen- 

 ium, and osmium belonged in a group to- 

 gether. It was later easily recognized that 

 cobalt, rhodium, and iridium furnished a 

 second triad, while nickel, palladium, and 

 platinum must also be grouped together. 

 The analogies between the three metals of 

 each of these groups is too patent to require 

 discussion, though incidentally we shall 

 have occasion to recur to it. When the 

 elements were arranged in the first periodic 

 tables, these metals did not fall into orderly 

 arrangement ; as late as 1878 the atomic 

 weight of osmium was considered greater 

 than that of iridium, platinum, or even 

 gold, while gold was given a weight less 

 than that of iridium or platinum. Cobalt 

 and nickel on one hand and iridium and 

 platinum on the other were considered to 

 have an identical atomic weight. The 

 seeming impossibility of reconciling these 

 nine metals with the periodic law is un- 

 doubtedly the reason why they were thrown 



