EXAMPLES OF THE FOUR METHODS. 461 



of that quality, is another circumstance which promotes the 

 deposition of dew ; but this third cause resolves itself into the 

 first, viz. the quality of resisting the passage of heat : for sub- 

 stances of loose texture " are precisely those which are best 

 adapted for clothing, or for impeding the free passage of heat 

 from the skin into the air, so as to allow their outer surfaces 

 to be very cold, while they remain warm within ;" and this last 

 is, therefore, an induction (from fresh instances) simply corro- 

 borative of a former induction. 



It thus appears that the instances in which much dew is 

 deposited, which are very various, agree in this, and, so far as 

 we are able to observe, in this only, that they either radiate 

 heat rapidly or conduct it slowly : qualities between which 

 there is no other circumstance of agreement, than that by 

 virtue of either, the body tends to lose heat from the surface 

 more rapidly than it can be restored from within. The in- 

 stances, on the contrary, in which no dew, or but a small 

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

 various, agree (as far as we can observe) in nothing except 

 in not having this same property. We seem, therefore, to 

 have detected the characteristic difference between the sub- 

 stances 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 interesting 

 speculation. 



We might now consider the question, on what the depo- 

 sition 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 though 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 



