1896.] on Chronographs and their Application to Gun Ballistics. 179 



of revolving cylinders ; also to demonstrate the accelerating force of 

 gravity. Thus, having attached the secondary wires of a coil to the 

 binding screw, and set the vibrating spring in action, a stream of 

 sparks passes through the suspended weight, the rapidity, which is due 

 to the note given out by the vibrating spring, being so great that to 

 the eye it appears as one continuous stream of light. But if the 

 weight be now dropped the sparks appear down each cylinder, opening 

 out as the weight descends. Each of these sparks gives its record on 

 the cylinders, and if they are read off by means of the velocity scale, 

 you will see that they are equi-distant as regards time but vary as to 

 linear distance. They follow the well-known law, 



An interesting experiment is simply made to test one's personal 

 equation, and to show the comparatively long time it takes for a 

 message to be sent from the brain to the fingers. Thus, if I press 

 this key, which breaks the primary circuit, the moment I see the weight 

 begin to fall, the induced spark will record the time it has taken to 

 perform this operation. 



We now pass on to instruments having revolving drums, the 

 circumferential speed of which can be made much greater than the 

 dropping weight, or plumb-bob, of the instrument I have described. 

 Prof. Bashforth's is a notable example, and one which did much good 

 work in experiments for ascertaining the resistance of the air to 

 projectiles.* 



After many years' work, designing and constructing chronographs 

 for experimental purposes, I devised the instrument shown in Fig. 2, 

 and the system of plugs, &c., with which I have been taking the travel 

 of shot up different guns during the last two or three years. In this 

 a large drum, made as light as possible consistent with strength, is 

 carefully mounted between coned centres. And here I may mention 

 an incident for the benefit of others, which might have had serious 

 consequences to myself. In the smaller and lighter instruments I had 

 previously employed, I had hard steel bearings v/orking into hard steel 

 centres, and found no difficulty with them, and I therefore employed 

 the same in this instrument. But one day, notwithstanding careful 

 lubrication, the two metals seized, and the drum, which was revolving 

 at a high speed, was quickly brought to a standstill and pulled out of 

 its bearings. I of course turned off the current at the first alarm, but 

 it was fortunate for me that the support held the drum. I now 

 employ No. 7 phosphor bronze, and all works smoothly ; at the same 

 time I do not neglect lubrication. This drum is revolved by means 

 of a motor, and this I consider a great advantage over any other 

 method, inasmuch as the drum can be driven at a very high speed, and 



* Description was here given of Professor Bashforth's chronograph and the 

 Noble chronoscope . 



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