MECHANICS AND USEFUL ARTS. 61 



preventing these disastrous occurrences. This is accomplished by 

 setting in motion in front of the locomotive a horizontal wheel which 

 with quick motion sweeps over the track. This wheel runs close to 

 the rails, and either throws aside the opposing obstacle at the instant 

 of contact, or if it falls upon the wheel, it is no less instantly disposed 

 of. The wheel is connected by gearing, to the front axle of the loco- 

 motive, and receives a swift circular motion from its movement. An 

 apron of plate iron is wrapped round in front covering about one 

 half of the disc of the wheel and presenting the convexity of its arch 

 forward; so that any object falling upon the wheel is instantly brought 

 against the opposing front of the apron. This, sloping back at the 

 side, the quick motion of the wheel instantly throws the object side- 

 ways from the track. N. Y. Farmer 8f Mechanic. 



STRAINS UPOX THE DIAGONALS OF LATTICE BEAMS. 



THE London Journal of Arts and Sciences gives an account of 

 experiments recently made in London upon lattice beams. 



The experiments were made on a model 12 feet in length, so con- 

 structed that the diagonals in compression, (which were strips of 

 mahogany, let into the top and bottom, but not fastened to them, and 

 the ties which were of hoop iron chains,) must of necessity take their 

 respective bearing and strain ; and by the substitution of a dynamo- 

 meter for any one of the ties, the strain on it could be accurately 

 measured. 



The results of the investigation were, that for a parallel beam of 

 one span, supported at each end and loaded at the centre, the strains 

 throughout the diagonals were uniform, and the horizontal strains 

 were greatest at the centre, decreasing uniformly at the points of 

 support. For a similar beam, uniformly loaded over its entire length, 

 the strains at the diagonals commenced at the centre, increasing uni- 

 formly to the points of support ; while the horizontal strains decreased 

 from the centre to the ends in the ratio of the ordinates of a parabola. 

 These results were arrived at by different methods of reasoning, and 

 the formulae derived from them were stated to be applicable to the 

 more complex form of a closely intersected lattice, taking into consid- 

 eration the increased number of triangulations. 



OX THE FORM OF IROX FOR MALLEABLE IRON BEAMS, OR 



GIRDERS. 



THE following is an abstract of a paper read before the British 

 Association, by Mr. T. M. Gladstone: It is, said Mr. Gladstone, on 

 the application of wrought iron beams or girders I propose to make 

 some remarks, by contrasting their powers and properties with those of 

 cast iron ; to show what form of iron I conceive best adapted for such 

 use, and to state, as a manufacturer, what may be expected as the capa- 

 bilities of iron works to produce the same bpyond previous efforts, so 

 as to meet the increased requirements of the times. It is found that, 



