DISCOVERY BY EXAMINING EARE SUBSTANCES. 505 



substance, and every new combination of substances, must 

 possess new properties (otherwise we could not know them 

 to be new), and produce new effects, so it follows that rare 

 or peculiar substances are fertile sources of new dis- 

 coveries. 



Various important discoveries were made in thermo- 

 electricity by Peltier, Matthiessen, and others, by the aid 

 of the comparatively scarce substances, tellurium, sele- 

 nium, and bismuth. Eoscoe, by investigating compounds 

 of vanadium, discovered that that element was closely 

 allied to phosphorus, and determined its true atomic 

 weight, and found that the weight given by Berzelius 

 was not an accurate one. Arfvedson discovered lithia by 

 analysing petalite and spodumene. It was by minutely 

 examining the zinc ores of Frieberg that Eeich and Eichter 

 discovered indium ; and, by similarly examining the zinc 

 ores of the Pyrenees, Boisbaudran discovered gallium. 



After a new substance is discovered in one particular 

 place or rare material, it is frequently found in a great 

 many others. Thus the selenium of Fahlun was soon 

 found in the curious and rare products of the Hungarian 

 mines, and in the sublimates of Mount Stromboli. Soon 

 after thallium was discovered in one substance, it was 

 found in many others ; and a similar result occurred with 

 rubidium and caesium. 



i. By examination of the residues, &c., of manu- 

 facturing processes. This method has on many occasions 

 led to the discovery of new truths of science, and espe- 

 cially to the discovery of new elementary substances. By 

 examining the solution of crude platinum in aqua-regia, 

 obtained in his process of manufacturing that metal, Dr. 

 Wollaston discovered palladium. Smith son Tennant, also, 

 in the year 1802, tried to alloy with lead the powder left 

 from native platinum after a solution of all the platinum 



