8 Dr. Hare in reply to Professor Olmsted. 



jack— as represented in the preceding figure ; and also hav- 

 ing a kerf, cut by a saw, parallel to, and nearly equi-distant 

 from, the principal surfaces of the plank, and at right angles 

 to the incisions, productive of the fork. 



By means of the fork, the glass is easily held steady by the 

 hand of one operator. By means of the kerf, the string while 

 circulating about the glass is confined to the part, where the 

 separation is desired. As soon as the cord smokes, the glass 

 is plunged in water, or if too large to be easily immersed, 

 the water must be thrown upon it. — This method is always 

 preferable when on immersing the body, the water can reach 

 the inner surface. As plunging is the most effectual method 

 of employing the water, in the case of a tube I usually close 

 the end which is to be immersed. 



RATIONALE. 



If the friction be continued long enough, the glass though 

 a very bad conductor of heat, becomes heated throughout in 

 the part, about which the friction takes place ; of course, it 

 is there expanded ; while in this state, being suddenly refri- 

 gerated by cold water on the outside only, the stratum of 

 particles immediately affected contracts, while that on the 

 inside not being chilled, undergoes no concomitant change. 

 Hence a separation usually follows. 



Art. II. — Rejoinder of Dr. Hare to the criticisms of Prof. 

 Olmsted, with strictures on the singular opinion, that attrac- 

 tion of gravitation emanates from the sun, as heat does 

 from ignited carbon. 



In the last number of the American Journal of Science, 

 Professor Olmsted alleges that I have committed an oversight 

 in making Davy's hypothesis " wear a much more mechanical 

 aspect" than it did originally, and in " applying to it princi- 

 ples which have no bearing on it whatever." 



According to Johnson's Dictionary, mechanics is the ge- 

 ometry of motion, a science which shews the effect of pow- 

 ers, or moving forces, so as they are applied to engines, and 

 " demonstrates the laws of motion." 



The phenomena of heat being by Sir H. Davy ascribed to 

 motion, how can my arguments, shewing that they are not 



