ANOTHER LESSON FROM THE RADIOMETER. 



305 



experiments in full, the public could not have 

 failed to perceive that the test which I am 

 blamed for not trying would have been utterly 

 useless. I will, therefore, briefly describe these 

 experiments, which are given in detail, and illus- 

 trated with woodcuts, in the Quarterly Journal 

 of Science for July and October, 1871. To meet 

 the foreseen objection, that while the attention 

 of the observers was otherwise engaged, Mr. 

 Home might possibly slide his fingers along the 

 board, and thus obtain leverage, I placed a ves- 

 sel of water with its centre exactly over the ful- 

 crum of the board the extremity of which was 

 attached to the weighing-machine. To prevent 

 Mr. Home touching the bottom of the vessel, and 

 to lessen the possibility of " rhythmical agita- 

 tion," a copper basin, with several perforations 

 in its bottom, was supported on a retort-stand, 

 so as to dip into the water in the first vessel. 

 Into this basin Mr. Home plunged his fingers. 

 By this arrangement it was rendered impossible 

 for Mr. Home to obtain leverage — that is, if the 

 doctrine still holds good that water transmits 

 pressure equally in all directions. Further, the 

 copper vessel acting as a breakwater, any rhyth- 

 mical agitation set up by Mr. Home would be 

 much enfeebled before reaching the bottom of 

 the outer vessel. Yet, in spite of these precau- 

 tions, the depressions of the board were substan- 

 tially the same as when Mr. Home placed his fin- 

 gers on the wood. But I went still further. I 

 caused Mr. Home to place his hands not on the 

 board at all, but on the table on which the ful- 

 crum rested, first near the end of the board, and 

 then at distances gradually increasing to three 

 feet. Still, the balance recorded great variations 

 of pressure. Finally, while Mr. Home placed his 

 hands in the position just mentioned, witnesses 

 held both his hands and his feet. The result 

 was still the same, the balance indicating ebbs 

 and flows of pressure. I submit, therefore, that 

 Dr. Carpenter's test would have been here a mere 

 waste of time, and that I was fully justified in its 

 omission. Indeed, it was as unnecessary as a 

 determination of Mr. Home's " downward press- 

 ure " on the chair on which he was sitting, or on 

 his boots when standing. 



One most significant conclusion which might 

 be drawn, and which must surely suggest itself 

 to every man of science who reads the history of 

 the radiometer, is the importance of residual phe- 

 nomena. It is well known to chemists that of 

 late years new elementary bodies, new interesting 

 compounds, have often been discovered in resid- 

 ual products, in slags, flue-dusts, and waste of 

 20 



various kinds. In like manner, if we carefully 

 scrutinize the processes either of the laboratory 

 or of Nature, we may occasionally detect some 

 slight anomaly, some excess or deficiency of ac- 

 tion, some unanticipated phenomenon, which we 

 cannot account for, and which, were received 

 theories correct and sufficient, ought not to oc- 

 cur. Such residual phenomena are hints which 

 may lead the man of disciplined mind and of fin- 

 ished manipulative skill to the discovery of new 

 elements, of new laws, possibly even of new 

 forces. Upon undrilled men these possibilities 

 are simply thrown away. The untrained physi- 

 cist or chemist fails to catch these suggestive 

 glimpses. If they appear under his hands, he 

 ignores them as the miners of old did the ores 

 of cobalt and nickel. That in the experiments 

 undertaken to determine the atomic weight of 

 thallium I should at once detect a slight anomaly 

 in the action of my very delicate balance, should 

 consider it worthy of the most minute and pro- 

 tracted investigation, and should follow up the 

 clew for so many years, is surely sufficient to re- 

 fute the charge of imperfect training advanced 

 by Dr. Carpenter at the close of his article in 

 the Nineteenth Century. The moral might have 

 been pointed with additional force by a reference 

 to my discovery of thallium itself, which was 

 likewise the result of the careful and systematic 

 examination of a chemical residue, in which, 

 when a mere boy, I had detected a chemical 

 anomaly, and noted it for further investigation. 



This great lesson — the importance of residual 

 phenomena — must be pronounced of the highest 

 moment to the student, and interesting, surely, 

 even to the multitude. Yet, Dr. Carpenter, ad- 

 dressing a highly-cultivated class of readers, 

 overlooks it altogether ! He gives, indeed, an 

 account of the " origin of these researches," and 

 pronounces it " rather singular," but the moral 

 he desires to point is of a totally different nature. 

 As I have said, Dr. Carpenter can draw but 

 one lesson from the analysis of my scientific re- 

 searches, and he insists that it is criminal to be 

 " ' possessed' of any ideas, or class of ideas, that 

 the common -sense of educated mankind pro- 

 nounces to be irrational." J But the " common- 

 sense of educated mankind " at one time denied the 

 circulation of the blood, and pronounced the earth 

 to be the immovable centre of the universe. At 

 the present day it upholds errors and absurdities 

 innumerable, and " common-sense " has been well 

 characterized as the name under which men deify 

 their own ignorance. Are scientific men never to 

 i Pa?e 256. 



