dulum, and determine both the initial velocity and the resistance by accurate observations of the angle, the range, and the time of flight. For the purpose of facilitating the solutions of the various problems which may arise in practice, auxiliary tables may be derived from the fundamental ones.

When a shot is fired in a steady breeze, the direction in which the ball meets the air is not the apparent direction of the gun, it is that of the resultant of the two motions, and the computations have to be made as for that resultant.

Thus if AZ (fig. 5) represent the horizontal direction of the gun, and AB the initial velocity of the ball projected on the horizontal plane, while bB represents the velocity of the wind, Ab will be the horizontal direction in which the ball meets the air. Since the vertical motion is not affected, the tangent of the elevation of the gun must be changed in the ratio of Ab to AB in order to get the tangent of the true angle of elevation in relation to the air, and Ab multiplied by the secant of that elevation is the true initial velocity.

If we now, using these corrected arguments, compute the hori zontal distances corresponding to equal intervals of time, measure those along the prolongation of Ab and from the successive points draw parallels cC, dD, &c., multiples of bB, we shall have the

horizontal projection of the ball's path, that path being a line of double curvature.

As an example of the variety and completeness of the information conveyed by such tables, we may cite the path detailed in the preceding table and represented by fig. 3.

The ball is projected from A with the velocity of 2.18, and at once encounters a resistance 4 times greater than its weight. The speed is rapidly lessened, and the path is deflected to become horizontal at V, where, in the present instance, the resistance is just equal to the weight. On account of this resistance the speed is still slackened, but gravity now comes to accelerate the motion downwards, and, at about the fifth interval from V, has overcome the retardation, thereafter the velocity slowly increases, and tends ultimately to reach the limit 1.00.

Those cases in which the characteristic angle A of fig. 4 is obtuse have little or no application to gunnery; in them the path is never horizontal, but is inclined downwards all along.

The analysis of these motions is complex, and the calculations thereon following are tedious, but the results, when tabulated, are of easy application. The theory would be uninteresting to those engaged in the actual business, just as the mode of construction of trigonometric and logarithmic tables is scarcely ever thought of by the navigator or surveyor. What we have at present to consider is the advantage to be gained by the compilation of a series of tables such as those sketched out.

3. On some Physical Experiments relating to the Function of By David Newman, Glasgow. Communi

the Kidney.

cated by Professor M'Kendrick.

(Abstract.)

This paper treats of the physical influences which promote the secretion of urine, as far as can be demonstrated by experiments upon animal membranes and the kidneys of animals recently killed. Before going on to consider the subject I may be permitted simply to mention the theory held regarding the means by which the

kidney performs its function, and also say a word or two in connection with the structure of that organ. As regards its histology the kidney may be said to be composed of two elements-(1) the bloodvessels, and (2) the tubuli uriniferi. (This is leaving out of account the lymphatic arrangement.) The kidney receives its supply of blood from the renal artery, which, as it passes into the substance of the kidney, penetrates the cortical portion and gives off branches. The uriniferous tubules in this part of the kidney end in globular dilatations called the capsules, or Malpighian bodies; it is into these that the branches of the renal artery pass to form convoluted coils, the glomeruli. The branches of the renal artery which pass into the glomeruli are called the afferent vessels, and the vessels that are formed by the reunion of the branches of the glomeruli are called the efferent vessels. After the efferent vessels emerge from the capsule of the Malpighian body they again subdivide to form true capillaries, most of which go to form a closely meshed network round the tubuli uriniferi. finally unite to form the radicals of the renal vein.

They

To make use of the description of Mr Bowman, "it would be difficult to conceive a disposition of parts more calculated to favour the escape of water from the blood than that of the Malpighian body. A large artery breaks up in a very direct manner into a number of minute branches, each of which suddenly opens up into an assemblage of vessels of far greater aggregate capacity than itself, and from which there is one narrow exit. Hence must arise a very abrupt retardation to the velocity of the current of blood." But besides this arrangement, by which a large volume of blood is exposed to circumstances the most conducive to free filtration of its fluid constituents, we have a condition, namely, the secondary capillary system on the distal side of the glomerulus, which, by its resistance to the onward flow of the blood, subjects the blood inside the Malpighian body to considerable pressure. It is now generally supposed that the excretion of urine takes place by filtration of a dilute solution of the soluble constituents of the urine through the glomerulus into the capsule of the Malpighian body. This weak solution then passes along the tubuli uriniferi, where it comes into close contact with the blood it has just left. It is then supposed that an interchange takes place between the blood in the capillaries surrounding

the tubules and the fluid inside by which a certain amount of the water passes again into the blood, and so leaves the urine in a more concentrated state than it was when it first passed from the glomerulus into the dilated end of the urine tubes (Ludwig). It is believed, however, that the epithelium, which lines the convoluted tubes, performs certain functions in connection with the secretion of the solid constituents.

The rapidity of the secretion of urine may be said to depend upon the following factors: (1) The relationship which exists between the pressure of the blood in the glomerulus of vessels and the urine in the capsule of the Malpighian body and in the tubuli uriniferi; (2) the state of the blood pressure in the venous system of the kidney; (3) the pressure upon the lymphatics; (4) the quality of the blood in the artery of the Malpighian tuft; (5) the state of the walls of the artery constituting the Malpighian tuft, and of the capsule itself, these being regarded as the filter through which the fluids and soluble constituents of the blood have to pass. The influence of vaso-motor nerves upon secretion must not, however, be forgotten; not only do they exert an influence upon the quantity and quality of the secretion by dilating or contracting the arterioles, but their influence upon the chemical processes, by reason of their communications with the secreting cells (Pflüger), must be remembered; (6) activity of tubular epithelium.

In the experiments I have endeavoured to imitate the conditions found in the Malpighian body of the kidney. I have not been able, however, to represent the lymphatic arrangement.

The apparatus, a drawing of which, kindly executed for me by my friend Dr Robert Moffatt, is shown in the following woodcut. It consists of a piece of rabbit's bowel A2 enclosed in a glass tube B2. To each end of the bowel a small glass T-tube is attached. One of those tubes is connected with a pressure-bottle A, and a manometer A1. The pressure exercised upon the fluid inside the bowel by the pressure-bottle and indicated by the manometer A1 will be designated the afferent pressure. The tube attached to the other side of the bowel conveys the fluid that passes along the bowel to the vessel B, and the pressure exercised upon the fluid which it contains, called the efferent resistance, is indicated by the manometer B1. Through a cork at the right hand side of the large tube, another

T-tube communicates, on the one hand, with the inside of the large glass tube containing the bowel, and, on the other, the vessel E and manometer C1. The vessel E will therefore contain the fluid that filters through the membrane A2.

The index in the manometer A1 will therefore represent the afferent pressure, and correspond to the arterial tension of the renal artery; B1 will indicate the efferent resistance (when applied to the kidney, the venous resistance), while the manometer C1 will show the resistance offered by the fluid in the tube B2 to the transudation of the fluid inside the bowel, and therefore correspond to the tension of the urine in the capsule of the Malpighian body.

In the first series of experiments water was passed into the bowel under an afferent pressure of from 10 to 50 mm. of mercury, the efferent resistance being the same in each experiment as the afferent pressure, so that no water passed along the bowel to B. The amount of fluid which transuded through the bowel was found to increase in accordance with the pressure used. It was shown that for every 10 mm. increase in the pressure, there was 533 c.c. more water filtered through the bowel per minute. Thus under a pressure of 10 mm. 2.133 c.c. transuded in a minute, and when a pressure of 50 mm. was applied 4.266 c.c. passed in the same time. From these results we would therefore conclude that the amount of fluid which transudes through an animal membrane is increased according to the tension of the fluid inside. In relation to this experiment, take the following:-Instead of an animal membrane the kidney of a recently killed horse was employed; in this case a three-quarters per cent. salt solution was used instead of water, as it