476 THE POPULAR SCIENCE MONTHLY. 



kinds of solid matter, and one liquid body, mercury, were known, 

 which afterward became recognized as elements. Between then and 

 the present time, 33 kinds of solid matter, and one liquid body, bro- 

 mine, have been added to the list the discovery of the earliest of them 

 occurring almost simultaneously with, or even just preceding, that of 

 the last discovered of the elementary gases. 



Among the number of bodies discovered prior to 1803, when Davy 

 effected the decomposition of the alkalies, several, at first thought to 

 be elementary, are now known to be compounds of oxygen with other 

 bodies still regarded as elements ; and conversely, two bodies, namely, 

 chlorine and fluorine, at one time thought to be oxides, have since be- 

 come regarded as elementary ; but in none of these cases did the dis- 

 covery of what is now considered to be the real constitution of the 

 bodies add or subtract an element to or from the list. 



From the period of the modern or Lavoiserian conception of ele- 

 ments and compounds down to the beginnnig of the nineteenth cen- 

 tury, the recognition of new elements occurred with much frequency 

 at short but varied intervals. After then, the discoveries became 

 somewhat less frequent ; but, even within the last 50 years, no fewer 

 than 12 new elements have been added to the list, being at the rate of 

 one new element every four years. Throughout, the periods of dis- 

 covery have been somewhat irregular in their occurrence. Thus, in 

 the years 1802 and 1803, six new elements were discovered, namely, 

 tantalum, cerium, palladium, rhodium, iridium, and osmium; within 

 the succeeding 14 years only one new element, but that a very impor- 

 tant one, namely, iodine ; and in the fifteenth and sixteenth years, three 

 new elements, namely, lithium, selenium, and cadmium. The longest 

 barren interval, one of 13 years' duration, took place between the dis- 

 covery of niobium, by Rose, in 1846, and that of csesium and rubidium, 

 by Bunsen, in 1859*. The last discovered of the elements, namely, 

 indium, being fully seven years old, and there being no reason to con- 

 sider our present list as any thing like complete, or to apprehend any 

 cessation of additions thereto, it is now quite time for some other new 

 element to be made known. For we may reasonably anticipate the 

 discovery of new elements to take place at irregular intervals possibly 

 for centuries to come, and our list of the elements to be increased at 

 least as much in the future as in the past. 



The fresh discovery, however, of any abundant elementary con- 

 stituent of the earth's crust would seem scarcely now to be expected, 

 seeing that of the 32 elements which have become known since the 

 year 17*74 the year of the discovery of chlorine and oxygen and man- 

 ganese and baryta the great majority belong to the class of chemical 

 curiosities ; while even the four or five most abundant of the since dis- 

 covered elements are found to enjoy but a sparing, although wide dis- 

 tribution in Nature, as is the case, for example, with bromine and 

 iodine ; or else to be concentrated but in a few specially-localized 



