1 GENERAL SUMMARY OF SCIENTIFIC AND 



presented to the Society of Aerial Navigation, which was most suc- 

 cessful. But a year later a mechanical bird was produced which es- 

 sentially solved the problem. 



Moreau has made a series of exj)eriments to determine the precise 

 function of the swimming-bladder of fishes. He shows very ingen- 

 iously that fishes which possess such a bladder undergo variations of 

 internal pressure, and hence that they do not, as is generally stated, 

 make use of muscular power to preserve their density unaltered when 

 this pressure cl^anges. The function of the swimming-bladder, then, 

 in Moreau's opinion, is to enable the fish to adapt itself to all depths, 

 not by a mechanical action exerted upon this by means of its mus- 

 cles, but solely by changing the quantity of air which is contained 

 in this organ. 



Wagner has made an investigation of the accuracy of the results 

 obtained with the effusion aj^paratus of Schilling for determining 

 the density of gases. Three perforated platinum plates were used, 

 having holes of different sizes. With coal gas the density was 0.46 

 with the largest, 0.47 with the mean, and 0.48 with the smallest 

 opening. Oxygen gave 1.21, 1.08, and 1.21 under these conditions, 

 the true density being 1.10. Hydrogen gave 0.22, 0.20, and 0.23, its 

 actual density being 0.069. Carbonic acid gave 1.51, 1.36, 1.36, in- 

 stead of 1.52. For gases other than coal gas, therefore, the method 

 is inaccurate. And even for this the variation from the actual den- 

 sity, as determined by the balance, was 0.03, a value of great impor- 

 tance so far as the illuminating power is concerned. 



Lecoq de Boisbaudran has proposed a simple form of cock for gas 

 or water. In the middle of a piece of small glass tube a plug is 

 firmly fixed, and a hole is bored into the tube on each side of it. 

 A short piece of larger tube is taken, a cork thrust into it about 

 half its length, bored to receive the first -mentioned tube. This 

 cork has a lateral opening. Both ends of the larger tube are 

 closed with corks, the smaller passing through them. If now the 

 hole in the smaller tube be opjDosite the lateral opening in the cork 

 within the larger tube, there will be a free flow of water or gas 

 through the whole ; but by rotating the tubes half round, the open- 

 ing in the tube is closed by the cork, and the flow ceases. 



ACOUSTICS. 

 Mercadier has published the results of his experiments on the vi- 

 bration of steel forks, from which he concludes, first, that the number 

 of vibrations of such forks, other things being equal, is independent 

 of their breadth ; second, that the number of vibrations is directly 

 as the thickness ; and, third, that this number is inversely as the 

 square of the length. These results are in comj)lete accordance with 

 those calculated from the theory of elasticity in solids. With re- 

 gard to the amplitude of the vibration as affecting its isochronism, 



