H. M. Bernard — Developing Trilobites. 



555 



be again shot up. Under these circumstances it was not easy to 

 manipulate the fossil, and the cutting action was not sufficient. 



The sand was then allowed to run out through the funnel, which 

 was connected by a short india-rubber tube with the nozzle of a 

 blow-pipe apparatus. The air was forced through a small aperture 

 just behind the feed, which, in this case, was sand instead of gas, 

 and further, the aperture of the nozzle itself was narrowed by 

 inserting a short piece of fine bore india-rubber tubing. The sand 

 was shot out by this arrangement, with much greater velocity, but 

 yet not with the highest possible, under the available pressure. 



Enlarged section of part of Apparatus for developing fossils by means of the Sand- 

 blast. Apparatus inmited by W. I. Last, Esq. (Keeper of the Machinery 

 Division), Science and Art Museum, South Kensington. 



"The action, being partly due to induced currents, the amount of 

 inert air carried along considerably reduced the velocity of the 

 combined jet." Various other difficulties also had to be contended 

 with — the dispersal of the sand, the clouds of fine dust, and, again, 

 the manipulation of the fossil. 



The final method planned and carried out by Mr. Last was the 

 most ingenious : in order to get still more force, the sand was con- 

 fined in a large bottle, but instead of being drawn into the air 

 stream as before, it was forced in by the air pressure within the 



