SIDE RODS.
Many attempts have been made to dispense with side rods, and they certainly are a troublesome part of the machinery to keep right; but no better means of connecting driving-wheels has yet been devised. The first method of coupling driving-wheels together, so that more than one pair might be available for adhesion, was by means of cogs and gearing. This was improved on by an endless chain working over pocketed pulleys; but even this was an extremely crude device,—working with tumultuous jerks, and a noise like a stamping-mill. One of the first real improvements, which George Stephenson effected on the locomotive, was the inventing of side rods. An essential element in locomotive construction needed to make side rods run with safety, is, that all the wheels connected shall be of the same circumference. There is a practice on some roads of putting new tires on wheels just as they come from the rolling-mill, without putting them in the lathe. Such tires are seldom accurate in size; and they cause no end of trouble, especially to side rods. This is one of the economical practices that does not pay.