Polytechnic Association Proceedings. 675 



nesia with a solution of the chloride of magnesium; the denser the 

 solution the harder will be the cement on drying. It has great 

 agglutinative power. One part of this magnesium compound mixed 

 with twenty parts of sand, will form a hard and solid block, whereas, 

 lime will not admit of being incorporated with rnore than two or 

 three parts of sand to form a blocli of equal hardness. It will also 

 be found to be the best material to use in connection with pebbles 

 in forming the walls of buildings. This cement might be made 

 on a large scale and very cheaply, at Syracuse, N. Y., and other 

 localities where the bittern from salt works is abundant, and lime- 

 stone can be readily converted into quicklime. 



ASTEROIDS. 



The recent discovery by Prof. Watson, of the University of 

 Michigan, of another small planet, lying between the orbits of Mars 

 and Jupiter, makes the total number of asteroids now known 

 ninety-three. There is reason to believe that many hundreds of 

 this interesting family of planets yet remain undiscovered. The 

 labor of observing so many of these bodies with the accuracy 

 necessary to compute their orbits, has become so great that unless 

 very energetic steps are taken by astronomers, many of the smaller 

 ones will escape their notice and again be lost. At the present 

 time two or three are missing, and owing to the fact that their orbits 

 had not been correctly determined, they will probably need to be 

 rediscovered when wanted. The method of designating planets 

 by names belonging to the ancient mythology, will have to be given 

 up should the discovery of new asteroids continue at the present 

 rate. Already these small planets have been numbered, and are 

 better kno^\^l to astronomers by their numerical designation than 

 by their classic appellations. 



THE BEAVER AS AN ENGINEER.. 



At the last meeting of the American Association for the Advance- 

 ment of Science, L. H. IMorgan, Esq., of Rochester, read an 

 interesting paper on the habits of the beaver. Having made this 

 animal the subject of study for several years, he was able to give 

 many interesting facts regarding the extent of their operations. 

 On the southern shore of Lake Superior, in Marquette county, he 

 found the remains of long canals and dams constructed by them 

 for the purpose of transporting their cuttings, consisting of trunks 

 of trees two or three feet long, from the place where the trees liad 



