1862.] 



21 



was bored at first to an elliptieity differing but little from a circle, 

 not, however, a true ellipse, but two semicircular arcs, on centres a 

 little separated, connected by straight lines at the periphery ; and 

 corresponding projectiles were made similarly differing from the true 

 form generated by an ellipse about its minor axis. The difference, 

 however, between the long and short axis of the figure of the shot 

 was insufficient to obviate its getting crosswise in the bore, by means 

 of the necessary windage to allow of free rolling in the bore. 



The mortar was then re-bored to its present dimensions, by the 

 kind aid, in lending instruments, of Mr. George Hoffman of Margate. 

 Fig. 3 represents a section of the bore in its present state. 



On this very small scale nothing, however, of any consequence could 

 be ascertained in either force or accuracy, though a singular result 

 appeared as to effect of relative position of centre of gravity ; for in 

 both models the longest ranges were afforded by a position of the 

 centre of gravity which was the reverse of that giving the longest 

 ranges in large guns. 



Ranges. 

 Longest. 



Second . 

 Third . 

 Shortest 



Large guns. Models. 



Above.. Below. 



Behind Behind. 



In front In front. 



Below Above. 



The reason seems to me, as regards the models, to be, that the 

 powder has more time for complete ignition in such very short 

 tubes when the shot is in stable equilibrium than when in the 

 reverse position. The mortars were used as guns at low angles. 



Fig. 5. Fig. 6. 



Side-view of disk of 5 ozs. Section of Yig. 7. 



Sphere of 5 ozs. 



Actual size. 



Section of 

 disk. 



I adapted one of them to project disks (figs. 5, 6) which were of 

 about the same weight (5 ounces) as the spheres (fig. 7) for the other 

 mortar. 



