1880.] NEW YOEK ACADEMY OF SCIENCES. 181 



of new forms of matter; an interest out of proportion perhaps to 

 the real vahie of the discoveries. Diirinii the hist nine years 

 chemists have not failed to sustain this interest, for they iiave 

 procLaimed no less than thirty-one new elementary bodies. 

 The ambition of these chemists, however, has been greater 

 than their accuracy, for of these thirty-one bantlings but 

 five or six have survived the scrutiny of the doctors, two or 

 three are now in precarious healtii, and the remainder have been 

 buried or cremated without ceremonies. Of the youthful sur- 

 vivors comparatively little is known; their character is being 

 severely tested, and their future destiny and utility is yet uncer- 

 tain. The extreme rarity of the minerals in which the new ele- 

 ments have been detected, the excessively small percentages of 

 the new ingredients, the extraordinary difficulties attending their 

 separation from known substances combine to render the in- 

 vestigations laborious, protracted, and costly. From twenty-four 

 hundred kilogrammes of zinc blende, Lecoq de Boisbaudran, 

 the discoverer of gallium, extracted sixty-two grammes of the pre- 

 cious metal; compared with this element, therefore, gold is both 

 abundant and cheap. Ytterbium, Scandium, Samarium, Thul- 

 ium, and the rest will long remain mere chemical curiosities 

 known to but few; probably the most sanguine will not claim 

 for them a future place among substances of economic value. ^ 



(4.) But of far greater importance than the elements them- 

 selves is the marvellous delicacy of the means used in detecting 

 and isolating them. When Bunsen and Kirchhof presented to 

 scientists the instrument which combines the penetration of a 

 telescope with the power of a microscope magnified an hundred- 

 fold, they were enabled to disclose nature's most hitUien secrets. 

 The new elements have been traced to their hiding-places, their 

 differences established, and their subsequent purity demon- 

 strated, chiefly by their emission and absorption spectra. Three 

 years ago,William Crookes, who had already discovered tliallium 

 by the atd of the spectroscope, announced a novel and remarka- 

 ble extension of the power of this instrument. Crookes' found 

 that many substances, when struck by the molecular discharge 

 from the negative pole in a highly rarefied atmosphere, emit 

 phosphorescent light of varied intensity. Having observed under 

 these conditions a bright citron-colored band or line, he pursued 

 the substance producing it, and, after a laborious search, found 

 that it belonged to. yttrium. Subsequent studies showed this 

 modification of spectrum analysis to exceed in delicacy all known 

 tests for tlie rarer earths ; yttrium can be detected when pres- 

 ent in one millionth part. AVithin a twelvemonth, Crookes has 

 made known the application of radiant matter spectrosco])y to 

 samarium ; the delicacy of this test surpasses that for yttrium^ 



