Troy Ounces Research Articles

The Prospector's Hand-book

THE general plan of this book was described on a preceding occasion, so that at present it is only necessary to notice the changes in the new issue. The work, we are told, has been thoroughly revised and enlarged. The enlargement consists of about eight pages of descriptive matter, mainly referring to South Africa; but the results of the thorough revision do not appear to be very considerable. Nearly all the mistakes and ambiguities in the original descriptions of metallic minerals are unchanged. The author calls attention to an addition descriptive of aluminium and its ores, from which we gather that bauxite is a ferruginous clay, a statement that is both original and incorrect. On pp. 94 and 96, one ton is said to contain 29,166 troy ounces, while in the table, on p. 121, 1 per cent., in an assay return, is given as equivalent to 326 ounces 13 dwts. 8 grains per ton. The latter statement is right, the former one is wrong, but the author does not attempt to explain the discrepancy. Perhaps he will do so in the next issue.

I. The Bakerian Lecture. Experiments upon the resistance of bodies moving in fluids

In a former Paper upon the Motion of Fluids, I stated the difficulties to which the theory is subject, and showed its in­sufficiency to determine the time of emptying vessels, even in the most simple cases; I also proved, by actual experiments, that, in many instances, there was no agreement between their results and those deduced from theory. The great difference between the experimental and theoretical conclusions, in most of the cases which respect the times in which vessels empty themselves through pipes, necessarily leads us to suspect the truth of the theory of the action of fluids under all other circumstances. In the doctrine of the resistances of fluids, we see strong reasons to induce us to believe, that the theory can­not generally lead us to any true conclusions. When a body moves in a fluid, its particles strike the body; and, in our theo­retical considerations, after this action, the particles are sup­posed to produce no further effect, but are conceived to be, as it were, annihilated. But, in fact, this cannot be the case; and what we are to allow for their effect afterwards, is beyond the reach of mere theoretical investigation. Whatever theory therefore we can admit, must be that which is founded upon such experiments as include in them every principle which is subject to any degree of uncertainty. We must therefore have recourse to experiments, in order to establish any conclusions upon which we may afterwards reason. In the paper above mentioned, I described a machine to find the resistances of bodies moving in fluids; since which time, I have made a va­riety of experiments with it, upon bodies moving both in air and water, and I have every reason to be satisfied of its great accuracy. In this paper, I propose to examine the resistance which arises from the action of non-elastic fluids upon bodies. This subject divides itself into two parts; we may consider the action of water at rest upon a body moving in it, or we may consider the action of the water in motion upon the body at rest. We will first give the result of our experiments in the former case, and compare them with the conclusions deduced from theory. Now the radius of the axis of the machine made use of in these experiments was 0,2117 in. the area of the four planes was 3,73 in. the distance of their centres of resistance from the axis was 7,57 in. and they moved with a velocity of 0,66 feet in a second. The first column of the following table exhibits the angles at which the planes struck the fluid; the second column shows the resistance by experiment, in the direction of their motion, in Troy ounces; the third column gives the resistance by theory, assuming the perpendicular resistance to be the same as by experiment; the fourth column shows the power of the sine of the angle to which the resistance is proportional.