SOME OF THE LATEST ACHIEVEMENTS OF SCIENCE. 151 



molecules, smashing- onto the surface, have their energy reduced and 

 that of the target corresponding!}' increased. The energy thus gained 

 seems to be employed partly in dissociating some of the molecules of 

 the gas (or in inducing some other condition which has the effect of 

 rendering- the neighboring air in some degree a conductor of electricity) 

 and partly in originating- an undulation through the ether, which, as 

 it takes its rise in phenomena so disconnected as the impacts of the 

 molecules of the air, must furnish a large contingent of light waves 

 of short wave-length. The shortness in the case of these Becquerel 

 rays appears to approach without attaining- the extreme shortness of 

 ordinary Rontgen ravs. The reduction of the speed of the quick- 

 moving molecules woidd cool the lnyev of air to which they belong, 

 but this cooling would rapidly be compensated by radiation and con- 

 duction from the surrounding- atmosphere. Under ordinary circum- 

 stances the difference of -temperature would scarcely be perceptible, 

 and the uranium would thus appear to perpetually emit rays of energy 

 with no apparent means of restoration. 



The total energy of both the translational and internal motions of 

 the molecules locked up in quiescent air at ordinary pressure and tem- 

 perature is about 1-1(),000 foot-pounds in each cul)ic yard of air. 

 Accordingly, the quiet air within a room 12 feet high, 18 feet wide, and 

 22 feet long contains energy enough to propel a one-horse engine for 

 more than twelve hours. The store drawn upon naturally by uranium 

 and other heavy atoms onl}^ awaits the touch of the magic wand of 

 science to enable the twentieth century to cast into the shade the mar- 

 vels of the nineteenth. 



While placing before you the labors and achievements of my com- 

 rades in science, I seize this chance of telling you of engrossing work of 

 my own on the fractionation of yttria, to which for the last eighteen 

 years I have given ceaseless attention. In 1883, under the title of 

 "Radiant-matter spectroscopy," I described a new series of spectra 

 produced by passing the phosphorescent glow of yttria. under molec- 

 ular ])ombardment in vacuo, through a train of prisms. The visibh^ 

 spectra in time gave up their secrets, and were duly embalmed in the 

 PhilosophicalTransactions. At the Birmingham meeting of the Brit- 

 ish Association, in 1886, I brought the subject before the chemical 

 section, of which 1 had the honor to be president. The results led 

 to many speculations on the probable origin of all the elementary 

 bodies — speculations that for the moment I nuist waive in favor of 

 experimental facts. 



There still remained for spectroscopic examination a long, tempting- 

 stretch of unknown ultra-violet light, of which the exploration gave 

 me no rest. But I will not now enter into details of the (juest of 

 unknown lines. Large quartz prisms, lenses and condensers, specially 



