162 ANNUAL OF SCIENTIFIC DISCOVERY. 



A NEW METHOD OF MEASURING DISTANCES. 



AN invention, by Capt. Groetares, of the Belgian Engineers, has 

 lately been tested at Greenwich. It is a simple means of ascertaining 

 the distance of any object against which operations may have to be 

 directed, and is composed of a staff, about an inch square and three feet 

 in length, with a brass scale on the upper side, and a slide, to which 

 is attached a plate of tin, six inches long, and three wide, painted red, 

 with a white stripe across its centre. A similar plate is held by an 

 assistant, and is connected with the instrument by a fine wire. When 

 an observation is to be taken, the observer looks at the distant object 

 through a glass fixed on the left of the scale, and adjusts the striped 

 plate by means of the slide ; the assistant also looks through his glass, 

 standing a few feet in advance of his principal, at the end of the wire, 

 and, as soon as the two adjustments are effected and declared, the distance 

 is read off on the scale. In the three trials made at AVoolwich, the 

 distance in one case, although more than 1000 yards, was determined 

 within two inches ; and, in two other attempts, within a foot. It is 

 obvious that such an instrument, if to be depended on, will admit of 

 being applied to other than military surveys and operations, and may 

 be made useful in the civil service. 



ON THE PROPER FORM OF THE MOULD-BOARD OF THE PLOUGH. 



AT the American Association, Albany, Prof. Hackley, of New York, 

 stated that he had received a communication from the N. Y. S. Agri- 

 cultural Society, requesting him to ascertain, if possible, the true theo- 

 retic form of the mould-board of the plough, so that it would offer the 

 least resistance, and thoroughly perform the work ; and to include, if 

 it could be done, the modification suitable to produce the pulverization 

 of the soil. Theory and experiment show that the angle of inclination 

 of the edge of the share, which cuts off the furrow slice from the bot- 

 tom, to the direction of the plough's motion, and that of the coulter, 

 which cuts off at the side, to the horizon, are matters of little impor- 

 tance. The advantage of inclining them is, that they may act like a 

 saw to cut off roots. The resistance to the action of these two portions 

 of the plough is uniform, and is the chief resistance to the draughts. 

 However, the general wedge-like form of the plough indicates that the 

 greater its length, (since the breadth is fixed by the required breadth 

 of the furrow,) the less the resistance, because the angle of the wedge 

 would thus be rendered more acute. Four feet is the utmost length 

 that would be consistent with the convenience of turning at the end of 

 the field. The longest Scotch ploughs are not more than three feet 

 nine inches, and the American ploughs are much shorter. The shares 

 and mould-board form properly one continuous surface. After the 

 furrow-slice is cut off by the coulter and front edge of the share, (which 

 latter w r e may suppose a line perpendicular to the direction of the 

 furrow and equal to its breadth,) the furrow-slice is to be lifted 

 and turned over, revolving about its edge. As this effect is to be pro- 

 duced by the mould-board in contact with the whole breadth of the 



