This blog is named after a series of articles written by Doctor P. H. Van der Weyde and published in Manufacturer and Builder Magazine in 1889 and 1890. The more I learn about Doctor P. H. Van der Weyde -- I'll share more about him in future posts -- the more I like him. My favorite parts are the introduction and the footnote. Here is the first of four parts.
The text is taken from the Library of Congress' American Memory site (http://memory.loc.gov/ammem/index.html).
The Pneumatic Rolling-Sphere Carrier Delusion.
BY DR. P. H. VAN DER WEYDE.
Manufacturer and Builder Magazine, Volume 21, Issue 10, October 1889
Many years ago I made the suggestion that one of the most useful books to be published for the benefit of inventors, would be a "Cyclopaedia of Failures." The conception of this idea was simply due to the observation that many ambitious and industrious inventors are blindly experimenting in fields which have been exhausted by others, and in which reasonably no success is to be expected, but who, in utter ignorance of what others have done, are repeating the same attempts and blunders. There is no doubt that in some cases at least partial success might have been achieved if such inventors had been informed of the difficulties encountered by other searchers in the same field, and of the means by which they had been partially surmounted.
It would, however, be a very difficult matter to obtain the information here referred to, as no inventor feels inclined to disclose his failures, much less to confess his incapacity or obtuseness, especially if the information were to be given for the benefit of others, because inventors, as a class, are jealous and mistrustful. The consequence is, that it would be a hard task to obtain the material required for the compilation of a Cyclopaedia of Failures, since it is only the successful labors that are published broadcast, for only in such cases will the inventors have taken the precaution to protect themselves by patents. In case this has not been done, the invention is frequently kept secret, particularly in cases where it can be applied as the means of money-making without divulging the nature of the process. Then the successful experiments share the same fate as the failures -- secrecy; with this important difference however, that they may enrich the inventor, while the failures more frequently impoverish him. If there were such a cyclopaedia as here referred to, and if it were consulted, many cases of destitution might have been prevented.
However, it must be considered that the failure of an experiment is frequently fully as instructive as its success, if not more so. This is a fact acknowledged by every experimenter in physics and chemistry, while in the mechanical arts the same circumstances are prevalent, so that the lesson taught by the failure of many a mechanical device benefits the experimenter alone, and is lost for the rest of the world, when the latter is kept in ignorance of the results which did not satisfy the expectations of the contriver.
The above introductory remarks are especially applicable to the repeated revivals of the attempts to construct pneumatic dispatch systems, of which the characteristic feature is the use of large rolling spherical carriers. Of these attempts I will now give an account, in so far as they have come to my knowledge:
My attention was first called to the subject in 1862, by Major R. Smith, who then was director of the Cooper Union, where I filled the position of Professor in Physics, Mechanics and Chemistry. He described to me experiments made ten years previously at West Point, where he was for some time Professor of Mathematics, and which experiments were intended to compare the velocity of propulsion by gravity along an inclined plane, where various bodies were made to slide or roll down.
At that time (some forty years ago) the mountain called Crows' Nest was covered with a dense forest of large trees, and a slide of logs had been constructed from nearly the top of the mountain, almost 2,000 feet high, to the river's edge, for the purpose of passing down the trunks cut by the woodmen. The enormous velocity attained at the end of their career when reaching the water, led perhaps to the problem if a ball would not attain still greater velocity when rolling motion was substituted for sliding friction? As so colossal and rough a slide was very inconvenient, or rather unmanageable, for experimental purposes, a temporary short slide was made, for which the hilly surroundings of that locality gave a ready opportunity; and it was soon found that the velocity attained by large rolling bodies did not quite come up to the expectations of those who looked for a much greater velocity.
At the time when these experiments were being conducted, a problem was published, which attracted the attention of the West Point professors as well as of students. It was as follows: Given, a solid silver ball of the same size as a gold ball; the latter is made hollow, so as to reduce its greater weight and make it equal to that of the silver ball; both are made to roll down an inclined plane. Question: Which will roll the faster?
The answers were of three kinds. Some said the silver ball would arrive first; others said the gold ball; and again others, and the majority, held that, as they were exactly of the same size and weight, their velocity would be exactly the same, and they would, therefore, arrive at the same time at the base of the inclined plane.
The experiment was made with large, solid, iron shot, and leaden balls of the same size, but cast hollow, so as to give them the same weight as those of iron; and it was found that the iron balls invariably ran the fastest and arrived at the base of the plane first.
In order to make this interesting experiment adapted to classroom demonstration for my students in mechanics, I modified it in this way: I turned two solid equal wooden disks of about eight inches diameter, and thick enough to roll on their edge without falling sideways. On each side of one of the disks I turned, very near to the circumference, a deep groove, and filled it up by casting lead in it. In the other disk I turned a hole in the center, of such a size that when also filled with lead, the weight of the two disks was equal. When, now, these two disks were placed at the upper end of an inclined plane, of say 25 feet in length, and started at the same time, the disk filled with lead at the center outran the other, and invariably arrived at the base of the incline first, no matter if it was made steep or nearly level. The reason is, that in the disk having its heavy charge near the circumference, every particle of this charge is compelled to describe a number of cycloids of some 7 inches vertical diameter; but in the disk charged near the center, the cycloids are very small, while at the very center the charge moves in a straight line towards its destination. It is clear that in the first case a large portion of the moving, force (gravitation) is consumed by producing cycloidal motion, while in the second case the moving force is applied in a more direct and economical manner.
This view was further verified by placing such a disk on one of the little wagons found in almost
every cabinet of physical science, in the set intended to illustrate the laws governing the equilibrium of bodies on inclined planes; either of them far outdid their former rolling performance. The reason is, that then every particle of matter contained in them is enabled to move in a straight line directly to the end of its career, so that the whole of the moving force is utilized for this purpose, without being compelled to produce additional circular or cycloidal movements.
The results were still more striking when each of the wooden disks was provided with an iron axle passing through its center, and these axles placed on two inclined rails. By this arrangement, the progressive motion was considerably retarded, while the rotating motion was as much increased, for the reason that the disks remained a much longer time on the incline. When this was not steep, and the disk which was charged with lead near its circumference was started first, it was always overtaken by the other disk when this was started not too long afterward, and both would mutually arrest one another by circumferential friction.
When at the base of the inclined rails horizontal rails were arranged, the disks, after leaving the incline, would run forward on the horizontal rails by their acquired rotary momentum; but the disk with the lead charge near the circumference, which progressed slower on the incline, would run faster and further on the horizontal plane than the disk with the lead charge near the center, for the simple reason that the former, during its descent, had obtained a much greater rotary momentum than the latter.
I also made, for my own instruction, some experiments with hollow balls filled with liquids, and found, as expected, a complication of circumstances which affected the results in various ways. They differed according to the nature of the contents, the amount of filling, the interior smoothness of the ball, etc. When filled with water, the hollow ball frequently outran a solid wooden one, as gravity made the shell descend without causing the immediate rotation of all the contents, aided as it was by the small frictional resistance between the water and the smooth solids, and of the water particles among themselves. Interior roughness caused retardation, as also did the partial filling of the ball with water, and more so when filling it with a gelatinous or viscous liquid. The latter peculiarity is easily verified and illustrated by watching the comparative behavior of two eggs, of which one is fresh while the other is boiled hard, and trying to spin them like a top (but sideways) on the tablecloth; the fresh egg, with its viscous contents, will scarcely make two rotations, while the hard-boiled egg, with its solid contents, will easily make twenty or thirty rotations. The cause is, that the rotary motion given by the hand to the hard egg is at once communicated to the whole mass, while in the fresh egg the motion is only communicated to the shell, and the viscous contents cannot at once receive the impulse, but by their inertia remain almost at rest, and afterward act like an interior brake on the rotating shell.*
The considerations and experiments above detailed, settled in my mind the question in regard to the non-advisability of using rolling balls for the transportation of matter, to which were to be added some other not less, if not even more, important considerations in regard to the manner in which the space inside the rolling balls should be filled up with the material to be transmitted.
1st. The balls must be entirely full and well packed, as otherwise the rolling movement will cause displacement and mutual friction of the contents, which may seriously damage them, especially when we take into account the rapid revolution incident to a velocity proposed of 150 miles an hour, which, for a ball of 80 inches diameter, would be not less than 800 revolutions per minute.
2d. The packing of the material must be not only tight, but also uniformly distributed in regard to its specific gravity, otherwise one side of the ball would be heavier than the other, and the ball could not roll straight, but continually knock sideways against the walls of the tube. Any mechanic who has experienced the trouble consequent upon the use of revolving wheels out of balance, especially such as revolve with such velocity as the dynamo-armatures -- 800 revolutions per minute, and as has been seriously proposed by inventors in this department -- will fully realize the impracticability of making the contents to balance, not to speak of the continual injury to which an unbalanced ball would subject the interior of the tube.
3d. The latter danger is increased by the fact that in all rolling bodies, every part which comes at the top moves forward with double the velocity of the center, while the part which comes in contact with the floor is temporarily at rest, only the center is moving directly forward. This fact alone must in the course of time exert a destructive effect upon the tube, especially as there must be sufficient space left between the ball and tube so as to allow this free motion without too much frictional collision.
4th. The necessary space will, under certain unavoidable circumstances, annihilate the air cushion between the balls, which it is claimed will prevent them from coming in mutual contact. These circumstances are as follows: Whenever a ball comes on an ascending grade, its gravity will counteract its progress, and the ball following it, being still on a level, will gain on it, and air will escape around the ascending ball. It is self-evident that a reliable air cushion can only be maintained by a hermetically-sealed contact, except where a very short duration is sufficient, as is the case when the carrier is arrested at the end of its course.
5th. When, from any cause whatsoever, two balls come in contact, a serious impediment to progress is effected, as at the point of contact the surface of the preceding ball moves rapidly upward, while that of the following ball moves just as rapidly downward, which will act like a brake on the rolling motion, and cause a partial sliding over the track, which will end in the next following ball overtaking the retarded couple, and a choking up of the tube will result.
So much respecting theoretical considerations. In my next article I will give a historical account of the attempts made with rolling carrier balls and their constant failure.
* I have placed for inspection at the office of the MANUFACTURER AND BUILDER, the identical wooden disks, charged with lead, as referred to above; also the eggs. The latter, however, are not the original.
Continued
No comments:
Post a Comment