MECHANICS AND USEFUL ARTS. 95 



of Philadelphia, for a device for relieving the feet of horses from the con- 

 cussion to which they are liable iu passing over pavements. It consists 

 in combining with the shoe a layer of India-rubber and what is called 

 hoof-plate, the rubber being placed between the shoe and the hoof- 

 plate, and the hoof-plate attached to the foot. By this arrangement, 

 while the rubber is removed from contact with the foot, and is so secured 

 as to be permanent and durable, its elasticity is at the same time made 

 available. 



New Ploughing Machine. A novel ploughing machine has recently been 

 patented by R. F. Hudson and H. G. Pomeroy, of New York City, which 

 operates as follows : 



"We may suppose two cart-wheels with gearing upon the inner face of the 

 spokes which drives three shafts hung in an oscillating frame, and lying 

 back at the rear of the axle, by which three furrows, each a foot wide and 

 a foot deep, are not only to be turned over, but thoroughly stirred up and 

 pulverized; the operation being something like Avorming a screw through 

 the soil, in so rapid a manner that it keeps the earth flying around in a 

 circle, and that of the three diggers mixing through each other. 



ON THE DECAY AND PRESERVATION OF BUILDING MATERIALS. 



The following is an abstract of a recent lecture before the Royal Institu- 

 tion of Great Britain, on the above subject, by Prof. Austed. 



He commenced by directing attention to the state of the stone in many of 

 the principal buildings in England and on the Continent, illustrating the 

 extreme irregularity with which various- materials, and even various sam- 

 ples of the same material, resist the action of the weather, and fall into 

 decay. He then described the chief building materials, explaining in each 

 case the cause of decay. Commencing with a general remark, that all 

 stones are rotten and weathered at the top of a quarry, or near an earthy 

 surface, and that the action of the weather on them is in some measure 

 thus indicated, he first alluded to granite. He stated its properties of hard- 

 ness and great durability in ordinary cases, but remarked that when soda 

 replaced potash in the felspar, the crystals of felspar were subject to the 

 action of the weather, and that, from some cause little known, the silica 

 base also occasionally failed. Still, the great practical objection to the use 

 of granite is its cost. Passing next to the sandstones, he defined them, 

 mentioning the chief varieties. He stated that the nature of decay in sand- 

 stones was generally the failure of the cementing medium, which is some- 

 times silicious, but more frequently calcareous, or clayey, or even oxide of 

 iron. He pointed out as the causes of decay, the want of sufficient cohe- 

 sion in the cementing medium, the nature of the cementing medium itself, 

 and the effect of expansion and contraction of water absorbed by the stone. 

 The limestones were next considered, and the principal varieties passed 

 briefly under review. They are all freestones, some are crystalline, others 

 semi-crystalline, but most of them are earthy, or oolitcd and absorbent. 

 They consist of particles of carbonate of lime, whether grains, as in the 

 case of chalk, or accumulated lumps, like oolite or roe-stone, or fragments 

 of shell ; and these particles are cemented together by carbonate of lime. 

 The stones are generally laminated, though the bedding is often extremely 

 obscure. When exposed to the action of the air in towns, they absorb 

 moisture and acid gases very readily, and the result is a gradual destruction 



