MECHANICS AND USEFUL ARTS. 121 



it, as do the common saws. The result is that the stuff comes from the saw 

 with its surface planed off about as smooth as can be done with a smoothing 

 plane. Saws thus made are adapted for all kinds of work, splitting, cross- 

 cutting, &c., no change at all in the set being required. 



Improvements in the Manufacture of Saws. The usual method of tempering 

 saws is to heat and then dip them in oil. This process is slow, laborious, 

 and costly ; it is also disadvantageous, because the saws become warped, and 

 require to be hammered up straight again by hand. An improvement 

 recently introduced by Henry Waterman of Williamsburg, N. Y.. consists in 

 tempering and straightening the saws at one operation. This is done by 

 heating the saws to the proper degree, and then pressing them with a sudden 

 and powerful stroke between two surfaces of cold iron. Drop presses are 

 employed for the purpose. The mechanism required in this process, it will 

 have been observed, is quite simple, and not expensive. Its use effects an 

 important economy in the manufacture of nearly ah 1 kinds of saws, and also 

 improves their quality. 



HORSE BRAKES. 



When the animal muscles are employed in overcoming resistance, or, hi 

 other words, in developing power, certain effects are observed, among which 

 are a quickened pulse, improved health and spirits, and (if severe or long 

 continued) exhaustion or fatigue. This is the case in ascending a hill, drawing 

 a load on a level, giving motion to machinery, and generally wherever work 

 of any kind is performed ; but hi descending a ladder, or holding back a load 

 in descending a hill, there is a reverse action of the muscles, a kind of 

 absorption of power, the effect of which has never, we presume, been investi- 

 gated, as the phenomenon is comparatively rare, and is seldom prolonged 

 beyond a very few minutes. Carriages have recently been constructed in a 

 peculiar manner for the turnpike road over the summit of Mount Washington. 

 They are made to stand at different angles, so that the floors are always 

 nearly level, and they are provided with brakes operated at will by the 

 hand of the driver, or by the backward strain of the horses. The last feature 

 seems particularly worthy of attention, as it may prove advantageous in 

 general use. The brakes referred to are operated by a strap passing around 

 a pulley or ring in the forward extremity of the pole or tongue. At every 

 declivity the carriage, hi crowding forward upon the horses, tightens the strap 

 and brings the brakes in contact with the wheels. When it becomes neces- 

 sary to back the carriage, a bolt is dropped by the driver which renders the 

 brakes inoperative. 



IMPROVEMENT IN GLASSES FOR HOTBEDS, &C. 



The following is a recent French invention for economizing space and 

 expense. Glass plates united by India rubber cloth, are made to fold 

 up so as to occupy but little space hi transportation, but what is of 

 more importance, the cost is not a fourth that of bell glasses of the same 

 capacity. 



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