456 Additional Notes. 



each other, and the arctic ether is accuinulatcc! In one end of 

 an iron or steel har, which is then calied the north pole of 

 the magnet; and the antarctic ether is accumulaleti on the 

 other end of the har, which is then termed the south pole of 

 the magnet, they become capable of attracting ot})er pieces 

 of iron or steel, and are thus cognizable by experiments. 



4. It seems probable that it is not the magnetic ether itself 

 ■which artracLs or repels pairules of iron ; but liiat an attractive 

 and repulsive ether attends the magnetic ethers, as in the case 

 of the electric. 



5. While the two electiic ethers, when separated by na- 

 ture or art, combine, by chemical affinity, with explosion, 

 emit light and heat, and leave a residuum; the two magnetic 

 ethers, after being separated in like manner, combine by che- 

 mical affinity, but without explosion, and produce, by their 

 unioii, a neutralized fluid. 



Motion and Moving Forces. 

 Projectiles, p. 37. 



Benjamin Robins, of Great-Britaiii, certainly did more 

 to improve the science of military projectiles than any indi- 

 vidual, not to say than all other individuals, who had gone 

 before him. He made a great number of well-devised and 

 important experiments; and, in his New Principles of Gun- 

 nery, left a lasting monument both of genius and labour. 



From the experiments detailed in this work, which was 

 published in 1742, it incontestibly appeared, that the resist- 

 ance made by the air to projectiles, which have a rapid mo- 

 tion, is much greater than had been supposed by Newton 

 and HuYGENS; that it is, indeed, so great, that the path de- 

 scribed by any shot whatever is very different from the curve 

 of a parabola, and, consequently, that all applications of 

 that conic section to gunnery are false and useless. Mr. Ro- 

 BiNs's experiments were made with shot of one ounce weight 

 only: it was, therefore, much to be wished, tliat such per- 

 sons as had opportunity miglit repeat the same experiments 

 with balls of a larger size. Mr. Charles Button, of the 

 Royal Military Academy at Woolwich, performed this service 

 to science. He even used in his experiments balls of from 

 twenty io fifty ounces weight. The result of these experi- 

 ments coatirmed Mr. Robins's principles in tlie most ample 

 manner. 



