EXAMPLES OF THE FOUR METHODS. 245 



down, cotton, &(•., as eminently favorable to the contraction of dew." 

 The Method of Concomitant Variations is here, for the third time, had 

 recourse to ; and, as before, from necessity, since the texture of no 

 substance is absolutely Hrm or absolutely loose. Looseness of texture, 

 therefore, or something which is tho cause 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 substances 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, there- 

 fore, an induction (from fresh instances) simply curruhorative 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 rajjidly 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 

 fi-om the surface more rapidly than it can be restored from within. 

 The instances, on the contrai-y, 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 difl'erence 

 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 aflibrded of this 

 indirect method, and of the manner in which the data are prepared 

 for it by the INIetliods 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 (juite sure that 

 the substances on which dew is produced differ from those on which it 

 i? not, in nothing but in the property of losing heat fi-om 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 import- 

 ance as might at first be supposed ; for we have, at all events, ascer- 

 tained that even if there be any other quality hitherto unobserved 

 which is present in all tlie substances which contract dew, and absent 

 in those which do not, this other pr(»perty must be one which, in all 

 that great number of substances, is present or absent exactly where the 

 property of being a better radiat(;r than conductor is present or absent ; 

 an extent of coincidence which af!brds the strongest presumption of a 

 community of cause, and a consequent invariable coexistence between 

 the two properties ; so that the property of being a better radiator 

 than conductor, if not itself the cause, almost certainly always accom- 

 panies the cause, and for purposes of prediction, no ciTor will bje 

 committed by treating it as if it were really such. 



Reverting now to an earlier stage of the inquiry, let us remember 

 that wo had ascertained that, in every instance where dew is formed, 

 there is actual coldness of the surface below the temperature of the 

 fiurrounding air; but we vieve not sure whether this coldness was the 



