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, bromine, 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 become regarded as elementary; but in none of these cases did the discovery 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 elements and compounds down to the beginnnig of the nineteenth century, 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 discovery 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 important 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 discovery 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 consider 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 constituent 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 1774—the year of the discovery of chlorine and oxygen and manganese and baryta—the great majority belong to the class of chemical curiosities; while even the four or five most abundant of the since discovered elements are found to enjoy but a sparing, although wide distribution in Nature, as is the case, for example, with bromine and iodine; or else to be concentrated but in a few specially-localized
