42 



und of placing it out of the power of the engineer to transcend the 

 assigned limit of pressure on the boiler. When it goes into action, it 

 stops the engine for the time, but permits the motion to be renewed 

 as soon as the cause of danger is removed either by the escape of 

 steam or the cooling of the flue. The alloy having again become 

 solid, the chain is passed round the cylinder anew, and the engine 

 pi'oceeds as before. 



Dr. Locke illustrated these remarks by successful experiments with 

 the working model. lie added, that the apparatus, with different mo- 

 difications which he described, has been applied to more than twenty 

 boats on the Ohio and Mississippi rivers, during a length of time suffi- 

 cient to test its practical usefulness, and that it is rapidly gaining 

 popularity with the proprietors of steam-boats, and with the public. 



Professor Bache, at the instance of Dr. Locke, gave a brief 

 history of the different applications of fusible metal to steam- 

 boilers. 



He stated that the experiments of the Franklin Institute had proved 

 the necessity of preventing the steam from pressing directly on the 

 fusible metal, in consequence of the liability of the metal to separate 

 into portions of different fusibility when submitted to such pressure. 

 He mentioned that Mr. Evans had adopted the same mode of apply- 

 ing fusible metal as the Committee of the Institute, and at about the 

 same time. Professor Bache then described the less perfect appara- 

 tus first devised by Mr. Evans, and alluded to one of his own which 

 he had himself published subsequently. He referred to the pecu- 

 liarities of the arrangement exhibited by Dr. Locke, and expressed 

 his satisfaction at the prospect of the safety guard being introduced 

 into general use, under the auspices of a practical mechanic like Mr. 

 Evans. 



Mr. Walker mentioned some strictures which he had re- 

 ceived from a correspondent, upon a paper, by Miss Morris 

 " On the Hessian Fly," now in the press of the Society, and of 

 which an abstract was published in its Proceedings for Decem- 

 ber last. 



Dr. Coates argued, that the history of the larva of the Hessian 

 Fly could by no means be considered settled; and that the sub- 

 ject was properly open for present and future examination. 



This he endeavoured to support by pointing out inconsistencies in 

 the descriptions of the best writers; remarking, that Mr. James Worth, 



