DISCOVERY BY MEANS OF NEW EXPERIMENTS. 525 



special methods, such as making experiments which other 

 persons have suggested ; modifying the experiments made 

 by others ; using known forces or instruments in a new 

 way ; making converse experiments to already known ones ; 

 examining the actions of particular forces on substances, 

 or those of substances on each other; subjecting series of 

 substances to new conditions; subjecting forces to new 

 conditions ; examining the effects of time upon phenomena ; 

 examining the effects of extreme force upon substances; 

 by employment of instruments of very great power, by 

 accurate quantitative experiments, &c., &c. 



In seeking to discover the cause of a given effect, we 

 have to devise and execute new experiments, in order to 

 be able to exclude each condition singly until all have 

 been excluded, and we are then said to work inductively. 

 But in finding new truths by examining the effects of a 

 particular cause, and in the formation and consequent 

 discovery of new compounds, and also in the production of 

 new physical or chemical effects by means of new experi- 

 ments, we work according to the deductive or synthetic 

 plan. The discovery of nearly all the compounds of sele- 

 nium, thallium, rubidium, caesium, indium, and of those 

 of the other elementary bodies, are instances of this kind. 

 In former times also, nearly all new organic substances 

 were found by means of analysis, but in recent years a 

 very large number have been formed and discovered by 

 synthetical methods. 



The method of making discoveries by devising and 

 executing new experiments has been a most prolific one, 

 and the number of new truths found by this plan is so 

 great that I must limit my selection. 



It was mainly by means of a well-devised experiment, 

 viz., having one of Torricelli's barometers carried to the 

 top of a mountain, that Pascal was enabled to discover 



