496 INDUCTION. 



instances, on the contrary, in which no dew, or but a 

 small quantity of it, is formed, and which are also 

 extremely various, agree (so far as we can observe) in 

 nothing except in not having this same property. We 

 seem, therefore, to have detected the sole difference 

 between the substances on which dew is produced, 

 and those on which it is not produced. And thus 

 have been realized the requisitions of what we have 

 termed the Indirect Method of Difference, or the Joint 

 Method of Agreement and Difference. The example 

 afforded of this indirect method, and of the manner in 

 which the data are prepared for it by the Methods of 

 Agreement and of Concomitant Variations, is the most 

 important of all the illustrations of induction afforded 

 by this most interesting speculation. 



We might now consider the question, upon what 

 the deposition of dew depends, to be completely 

 solved, if we could be quite sure that the substances 

 on which dew is produced differ from those on which 

 it is not, in nothing but in the property of losing heat 

 from the surface faster than the loss can be repaired 

 from within. And, although we never can have that 

 complete certainty, this is not of so much importance 

 as might at first be supposed ; for we have, at all 

 events, ascertained that even if there be any other 

 quality hitherto unobserved which is present in all 

 the substances which contract dew, and absent in 

 those which do not, this other property must be one 

 which, in all that great number of substances, is 

 present or absent exactly where the property of being 

 a better radiator than conductor is present or absent ; 

 an extent of coincidence which affords the strongest 

 presumption of a community of cause, and a conse- 

 quent invariable coexistence between the two proper- 

 ties -, so that the property of being a better radiator 



