194 REPORT—1868. 
considered that the first requisite was to have the direction and velocity of the 
currents of water which accompany a ship’s motion determined by actual observa- 
tion. For this purpose he submitted to the Section a rough scheme of experi- _ 
ments, which, however, he wanted to get corrected by the experience of a Com- 
mittee of the Association. He suggested that a vessel of the corvette class should 
-(at separate times) be towed, and also driven by her own screw, instruments 
being used to measure both the power employed, the speed of the vessel, and the 
velocity and direction of the accompanying water, at various rates of speed. He 
pointed out serious difficulties in ascertaining the direction of the currents of 
water, and was unable to suggest for this purpose anything better than direct 
vision. The author exhibited certain instruments for assisting the eye in looking 
through the disturbed surface,—one of them being a common water-glass, a simple 
trumpet with a sheet of plate glass at the bottom, which was dipped below the 
water, the other being Arago’s scopeloscope. He also described an electrical log, 
patented by M. Anfonso, of Mende. But he thought all these things required 
further consideration. He proposed to apply for a Committee of the Association 
to discuss the subject, with a view of considering what experiments might best be 
made; andif the Committee were of opinion that satisfactory results might be 
expected from such experiments, then to memorialize the Admiralty to detail 
vessels and officers for the purpose of carrying them out in the course of the 
summer, 
On Dynamite, a recent Preparation of Nitro-glycerine, as a Blasting Agent. 
By A. Nosrt. 
The author stated that by mixing nitro-glycerine and powdered silica in the 
proportions of 75 per cent. of the former to 25 per cent. of the latter, a substance 
was obtained which, while it retained all the valuable properties of nitro-glycerine 
for blasting, was no longer dangerous, inasmuch as it could be handled freely, and 
did not explode by fire alone, or when accidentally subjected to percussion, He 
instanced experiments lately made at Glasgow and Merstham. A box containing 
about 8lbs. of dynamite (equal in power to 80 lbs. of gunpowder) was placed over 
a fire, where it slowly burned away; and another box with the same quantity 
was hurled from a height of more than 60 feet on the rock below, no explosion 
ensuing from the concussion sustained. It appeared that the explosion when required 
was produced by means of a percussion-cap, which acted both by percussion and 
by fire, the combination of the two producing the effect, whilst neither alone was 
effective. The value of the material as a blasting agent appeared to be very great; 
and if it be as safe as the author believes, it cannot fail to be of great assistance 
both to the engineer and the miner. 
On a Probable Connewion between the Resistance of Ships and their Mean Depth 
of Immersion. By Prof. W. J. Macauorn Ranxine, O.L., LL.D., F.RS. 
The author, after referring to previous researches of his own and of Mr. Scott 
Russell in relation to waves, stated that the object of his paper was to call the 
attention of the British Association, and especially of the Committee on steam- 
ship performance, to the probable existence of an element in the resistance of 
ships hitherto neglected, viz. that every ship is accompanied by waves whose _ 
natural speed depends on the virtual depth to which she disturbs the water*, and 
that consequently, when the speed of a ship exceeds that natural speed, there is 
probably an additional term in the resistance depending on such excess. The 
author suggests that suitable observations and calculations should be made in 
order to discover its amount and its laws. Amongst observations which would be 
serviceable for that purpose might be mentioned the measurement of the angles of 
divergence of the waye-ridges raised by various vessels at given speeds, and the 
determination of the figure of those ridges, which were well known to be curyéd; 
and amongst the results of calculation the mean depth of immersion as found by 
dividing the volume of displacement by the area of the plane of floatation, and that 
eet 
* Let & be the virtual depth of disturbance ; the natural speed of the waves is V/gh. 
