782 



SCIENCE. 



[N. S. Vol. XVIII. No. 4G8. 



3. Responding to ultra-violet rays only. 



4. Responding to Roentgen rays only. 



5. Responding to radium and ultra-violet 

 rays (not to Roentgen rays). 



6. Responding to radium and Roentgen 

 rays (not to ultra-violet rays). 



7. Responding to ultra-violet and Roent- 

 gen rays (not to radium). 



8. Responding to radium, ultra-violet 

 rays and Roentgen rays. 



It is our purpose, further, to examine 

 the same collections by the infra-red rays, 

 for comparison with the ultra-violet; as it 

 is quite possible that many minerals will 

 give response of some kind with the infra- 

 red that are not affected by the ultra-violet. 



As for mineralogical determination, no 

 large apparatus is necessary, as is iised in 

 medicine or for physiological investiga- 

 tions. In fact, very simple apparatus is 

 sufficient. Therefore, we are devising a 

 series of appliances such that the entire ap- 

 paratus may probably be purchased for 

 much less than one hundred dollars. And 

 a photometer-like meter to measure the dis- 

 tance of penetration of the X-ray, the 

 ultra-violet ray, and also the distance of 

 the penetration of radio-active bodies. 



"We are also preparing a list of minerals, 

 selecting those most readily obtainable, to 

 illustrate these phases of activity or inac- 

 tivity with the three useful accessories. 

 For a small expenditure any school or col- 

 lege can obtain them for comparative study. 



As the electric furnace has given us 

 carborundum, artificial graphite and a 

 series of absolutely new carbides, because 

 with it we have attained temperatures of 

 a height unknown before its introduction; 

 and as the production of low temperatures 

 has resulted in the liquefaction of all 

 known gases and assisted in the discovery 

 of new ones; so perhaps the application of 

 these forms of energy may give us the 

 means of identifying substances that have 

 escaped all our earlier methods of observa- 



tion; and it may be that we shall find 

 a new series of elements. We are cleai'ly 

 on the threshold of a new field of scientific 

 facts and perhaps generalizations and laws, 

 which may yield results in the twentieth 

 century as interesting and remarkable as 

 the electrical discoveries were in the nine- 

 teenth. Indeed, some have already dis- 

 carded atomic chemistry and assumed ionic 

 chemistry, while pioneers like Ci'ookes, J. 

 J. Thomson and Lodge vouchsafe ' protyle, ' 

 'corpuscles' and 'electrons,' with more or 

 less experimental verification, although 

 they do not quite reach Ostwald's meta- 

 physical view. 



Here we gratefully acknowledge the aid 

 given us in free access to the collections, the 

 construction of a special dark room, every 

 facility of the museum's workshops, the 

 encouragement and advice given by the 

 museum's able director. Dr. H. C. Biunpus, 

 and the attention and assistance of Dr. 

 L. P. Grataeap, Mr. L. L. Seymour and 

 Mr. Smith, of the mineralogical depart- 

 ment, and of Mr. Dahlgren, the museum 

 photographer. 



SUPPLEMENTARY NOTE: ACTINIUM. 



We have recently had the opportunity 

 of making some experiments with a small 

 amount of the exceedingly rare, novel, and 

 hitherto almost unobtainable, element, 

 actinium, described by Professor Debierne 

 in the Comptes Rendus, 1898. 



This actinium was a preparation of the 

 oxide, with an activity of 10,000 (uranium 

 being taken as unity), prepared by Dr. 

 Debierne, and sent to one of us through 

 the courtesy of Professor P. Curie. The 

 emanations from it seemed most profuse, 

 and although it had been exposed for two 

 weeks, in a paper package in the mail, yet 

 they were as energetic at the time of its 

 arrival, and one week after, as they could 

 have been at any time. The substance is 

 wonderfully radio-active; in the few ex- 



