EXAMPLES OF THE FOUR METHODS. 495 



that the quality of doing this abundantly (or some 

 cause on which that quality depends) is another of 

 the causes which promote the deposition of dew upon 

 the substance. 



" Again, the influence ascertained to exist of sub- 

 stance and surface leads us to consider that of texture: 

 and here, again, we are presented on trial with 

 remarkable differences, and with a third scale of 

 intensity, pointing out substances of a close firm 

 texture, such as stones, metals, &c., as unfavourable, 

 but those of a loose one, as cloth, wool, velvet, eider- 

 down, cotton, &c., as eminently favourable 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 firm or absolutely loose. 

 Looseness of texture, therefore, or something which 

 is the 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 sur- 

 faces to be very cold while they remain warm within;" 

 and this last is, therefore, an induction (from fresh 

 instances) simply corroborative 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 cir- 

 cumstance 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 



