PROCEEDmOS OP SOCIETIES. 243 



ciently great to destroy tlie cohesion of the surface of the material 

 operated upon. The external layer is carried against the under stratum, 

 and the material is crushed and disintegrated by a portion of its own 

 body. 



No one would think of attempting to make any impression on 

 granite with a piece of lead for a cutting tool, but leaden bullets fired 

 from a rifle will speedily perforate a granite block, and the flattened 

 bullets will have a hard coating of granite on the contact side, the 

 debris of the surface that has been disintegrated. This is the action 

 on a large scale ; and the appearance and effect is the same on glass on 

 such a minute one that it requires the microscope to demonstrate it. 



The President said that there were several specimens of the action 

 of the sand-blast upon glass placed upon the table for inspection ; ono 

 of them had a hole entirely through it, and upon another there was the 

 perfect pattern of a bit of lace. These effects were the result of well- 

 known dynamical laws, all that was required being hard resistance on 

 the part of the body to be affected, and a high velocity in the moving 

 particles. A yielding substance would damp the force of the concus- 

 sion, and would not be affected ; just the same, in fact, as in catching a 

 cricket ball its force is destroyed by drawing the hands back ; and it 

 was also well known that a suspended silk handkerchief would stop a 

 bullet. Just in the same manner the lace, from its yielding nature, 

 protected the glass, which was acted upon in all other parts by the 

 impact of the rapidly-moving grains of sand. 



Mr. Peter Gray thought it might be interesting to know that the 

 process was to be seen in action every day still, at the International 

 Exhibition. 



Mr. Wenham said that a great deal depended on the pressure em- 

 ployed to cause the blast; with the steam blower the patterns were 

 produced with great rapidity, but at the soiree, when only hand power 

 was employed, hardly any effect was produced. 



The President pointed out that the effect produced depended 

 mainly upon the velocity of the impinging body; a tallow candle 

 might be fired from a rifle with suflicient force to perforate a deal 

 board. 



Mr. Wenham said that the harder the substance the greater was 

 the pressure required ; corundum needed a pressure of 300 lbs. to the 

 square inch. 



The President said that this was of course a necessary consequence. 

 If the force were diminished the effect would proportionately cease ; if 

 the candle were fired with the tenth part of a charge, instead of pene- 

 trating the board it would simply be squashed against it. 



Mr. Charles Stewart exhibited under the microscope a beautifully- 

 prepared specimen of a spermatophore of the common squid (Loligo 

 vulgaris), and by means of black-board illustrations explained its struc- 

 ture and functions. He also described in the same manner the general 

 arrangement of the generative organs of the male cuttle-fish. 



Votes of thanks having been passed to Mr, Stewart and to Mr. 

 Wenham for their communications, the meeting was adjourned to 

 November 5th, 



