212 DISCOURSE ON THE STUDY 



ment the number corresponding to any new sub- 

 stance added to the list is determined, we have, 

 in fact, ascertained all the proportions in which it 

 can enter into combination with all the others, so 

 that a careful experiment made with the object 

 of determining this number is, in fact, equivalent 

 to as many different experiments as there are 

 binary, ternary, or yet more complicated combin- 

 ations capable of existing, into which the new 

 substance may enter, as an ingredient. 



(223.) The importance of obtaining exact phy- 

 sical data can scarcely be too much insisted on, for 

 without them the most elaborate theories are little 

 better than mere inapplicable forms of words. It 

 would be of little consequence to be informed, 

 abstractedly, that the sun and planets attract each 

 other, with forces proportional to their masses, 

 and inversely as the squares of their distances: 

 but, as soon as we know the data of our system, as 

 soon as we have an accurate statement (no matter 

 how obtained) of the distances, masses, and actual 

 motions of the several bodies which compose it, 

 we need no more to enable us to predict all the 

 movements of its several parts, and the changes 

 that will happen in it for thousands of years to 

 come; and even to extend our views backwards 

 into time, and recover from the past, phenomena, 

 which no observation has noted, and no history 

 recorded, and which yet (it is possible) may have 

 left indelible traces of their existence in their 

 influence on the state of nature in our own globe, 

 and those of the other planets. 



(224.) The proof, too, that our data are correctly 



