804 On the Present Stale of Experimental Acoustics, 



the total velocity of supply, which would be absolutely the 

 same at points 30° apart. The weights of the feeders being 

 borne by the cranks, it is of no consequence that they do not 

 absolutely compensate each other. 



The escape-valves open into the feeders in the best modern 

 work ; the supply then ceases without noise or shock when the 

 bellows is full. 



The principle here applied is that of making the feed of 

 wind itself steady ; the plan more commonly adopted has been 

 to employ appliances to overcome the effect of the unsteadi- 

 ness of the supply. 



The arrangement is, I believe, not new; but I do not know 

 of any particular instance where it is in use. It is suitable for 

 the employment of power. Governing arrangements can be 

 applied. 



It would be desirable that a lathe should form part of the 

 laboratory fittings. With this assistance the more expensive 

 and novel forms of apparatus might be constructed in the labo- 

 ratory itself — such as new forms of the siren, oscillating disks, 

 revolving stopcocks, clock governors, &c. 



The most suitable engine that I have seen for the purpose 

 is Rider's hot-air engine. This is worked by a certain definite 

 mass of air alternating between a hot and cold cylinder, the 

 two plungers working in cranks at right angles. It is the 

 most silent engine that I have seen; and the smallest size of £ 

 H. P. can be worked with a gas-burner. Independently of 

 its suitability for laboratory purposes, it is an extremely pretty 

 bit of practical thermodynamics. 



So far as I am aware, no laboratory has been fitted with 

 arrangements of the nature of those I have described. The 

 plan seems to me worth trying; and I hope before long to 

 make an effort to carry it out. 



The cost of the whole of the new apparatus is hardly likely 

 to amount to that of a set of tuning-forks of Konig and a 

 "soufHerie de precision " of Cavaille Coll together. It seems 

 likely to do away with the need of a great part of the expen- 

 sive apparatus formerly required for these purposes; but I do 

 not suppose that it will be desirable to be altogether without 

 the older apparatus. The experiments of Konig, for instance, 

 can hardly be said to be repeated unless they are repeated to 

 some extent under the original conditions; and the comparison 

 of different methods may be expected to lead to instructive 

 results. Electromagnetic forks are unquestionably of great 

 importance, and for some purposes cannot be replaced, though 

 for large departments of work we may with advantage find 

 substitutes for them. 



