206 THE POPULAR SCIENCE MONTHLY. 



however, did not keep straight on like the first, but ran a short way, 

 then returned, and then again followed a little farther thau the first 

 time. They were evidently scenting the trail of the pioneer, and 

 making it permanently recognizable. These ants followed the exact 

 line taken by the first one, though it was far out of sight. Wher- 

 ever it had made a slight detour, they did so likewise. I scraped with 

 my knife a small portion of the clay on the trail, and the ants were 

 completely at fault for a time which way to go. Those ascending 

 and those descending stopped at the scraped portion, and made short 

 circuits until they hit the scented trail again, when all their hesi- 

 tation vanished, and they ran up and down it with the greatest con- 

 fidence." 



That among groups like the Ecitons, in which the sense of sight 

 is imperfect, or even totally wanting, enhanced delicacy of scent and 

 touch must be required in compensation, may be taken as self-evident. 

 With the language of ants, and especially with a possible scent-lan- 

 guage, is connected the faculty by means of which denizens of the 

 same city recognize each other under circumstances of great diffi- 

 culty. In the battles which take place between two nations of the 

 same species, how, save by scent, do the tiny warriors distinguish 

 friend from foe? We are told by some older observers that if an 

 ant is taken from the nest, and restored after the lapse of several 

 months, it is alonce received by its companions and caressed, while 

 a stranger ant introduced at the same time is rejected, and generally 

 killed. To a great extent this has been confirmed by recent investi- 

 gators. The returned exile was not indeed caressed, but was quietly 

 allowed to enter the nest, while a stranger was at once greeted with 

 hostile demonstrations. It has been maintained that this power of 

 recognition is destroyed by water, and that ants will treat a comrade 

 as an enemy if he has received a drenching. This, however, is evi- 

 dently a mistake. To prevent rain from penetrating into the nests 

 of the agricultural ant, the guards block up the doorways with their 

 bodies, and are often drowned at their posts. But their companions 

 are not thereby preventedjfrom recognizing them, as they try to bring 

 the dead bodies to life. Quarterly Journal of Science. 



HISTORY OF THE DYNAMICAL THEORY OF HEAT. 1 



By PORTER POINIER. 



I. 



A RECAPITULATION of the various conjectures which have been 

 advanced in explanation of so ever-familiar a sensation as that of 

 warmth or heat, would neither prove particularly feasible nor inter- 

 esting ; for doubtless during the vast period of time which has elapsed 



1 Introduction to an unpublished work on Thermo-Dynamics. 



