1879.] on the ' Thunderer' Gun Explosion. 231 



of velocity is obtained at only one place for eacli discharge, and 

 tlius if there were any accidental variation in the weight, or in the 

 dryness, or in the circnmstances attending the ignition of the chai'ge, 

 discordant results would ensue. 



We owe to the study and to the inventive genius of Captain 

 Andrew Noble, F.R.S., an apparatus, the chrono$co})e, which enables 

 the inquirer to determine the velocity of the projectile within the 

 gun at as many points as he may deem necessary. Diagram 7 repre- 

 sents the chrouoscope ; you will see that it consists of a train of 

 wheelwork by which the smooth circumference of the final wheels 

 lettered A can be made to move with great velocity. As much as 

 100 feet per second are reached. 



Assume now that the circumferences of the wheels be clothed 

 with properly prepared paper bands, and that a wire be brought in 

 proximity to the paper on each wheel, and be so coupled up to 

 an electrical apparatus, that on the wire being broken in some part 

 of its length, electricity shall pass from the point of the wire through 

 the paper to the wheel, making a mark on the paper. Xext assume 

 that the wire, properly insulated, is applied to a suitable triiri^er- 

 like apparatus, such as is shown on the diagram, in the side ot'tho 

 bore of the gun to be experimented upon ; then if the shot be fired, 

 it will as it passes each apparatus push in the trigger, and will 

 thereby break the wire, and will cause a record to tie left on the 

 paper; and if, as suggested, several wires be applied to the gun, 

 say at ten points, these will be broken in succession as the shot 

 passes them, each rupture will make its own mark on its band of 

 paper on the edge of its wheel, and the velocity of that band bein^ 

 known, the varying distance of the marks from a common datum will 

 be a measure of time, and therefore of the velocity which the shot had 

 in passing each wire in the gun, and thus the varying pressures in 

 the gun can be calculated. I have said that a velocity as high as 

 100 feet or 1200 inches per second has been given to the circum- 

 ference of the wheels, and as by proper appliance the y^V^ of an inch 

 can be read oft', it is possible to detect intervals of time of less than 

 one-millionth of a second (actually -^^-^l^^-^^) in duration. 



The second mode of ascertaining pressure is shown on Diai^ram 8, 

 which exhibits a crusher gauge drawn one-half full size ; the actual 

 gauges both before and after use are on the table. You will see the 

 gauge is composed of a little solid cylinder of copper, ,\-,th of an incli 

 in area by ^ inch long ; this is held loosely by a spring in the centre 

 of a hollow steel cylinder, which cylinder is screwed into the end of 

 the bore or the side of the bore, or the base of the projectile as the 

 case may be, and is provided with an accurate but easily fitting 

 steel piston which bears upon one end of the copper cylinder, the othei* 

 end being in contact with the base of the hollow cylinder. When the 

 gauge is applied to the side of the bore the outer end of tlie steel 

 piston is fair with the surface of the bore, and for the time fi)rms 

 a portion of that surface, and thus it receives on its end as much 



