By Way of Explanation
To the editor of the Scientific American:
I am taking the liberty of enclosing a statement which you may care to use in the Scientific American or the Monthly, which is, to a large extent, a reply to recent criticisms of the rocket method upon which I am working.
I have received a number of requests from papers for a statement of this sort, but prefer to have it appear in a publication of recognized standing.
[Signed] R.H. Goddard.
Clark College, Worcester, Mass.
January 12, 1921.
Ever since, a year ago, announcement was made that a rocket was under development which should, in principle, be capable of reaching great altitudes, even as great as interplanetary distances, there have been numerous articles in magazines and papers of more or less authenticity.
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To date, there has been little published criticism, except in an article in the November 20 Graphic (London). Chiefly in reply to the latter, it is believed worth while stating the purposes and possibilities of the investigation, although the writer prefers working quietly rather than issuing statements.
First, regarding the possible study of conditions at a great height in the atmosphere: Mr. Morrell, in the Graphic article, considers it unlikely that any instruments could survive a fall from so great a height. The important point is that the instruments and rocket fall from rest, and that under this condition even a small parachute must be sufficient to maintain the velocity at a safe value.
Thus, in the original Smithsonian publication, Miscellaneous Collections, Vol. 1, No. 2, p. 51, a calculation, based upon the air densities that very likely hold at high elevations, shows that if instruments supported by a small parachute fall from a height of 100 miles, the velocity would be reduced to, and maintained at, a safe value even before the 20 mile level had been reached. Attention is called to the first successful sounding-balloon ascension in America, at St. Louis, 1904, in which instruments fell 10.4 miles without damage, even without a parachute.
But even if this could not be done, the suggestion made in the original paper of leaving a few charges in the rocket to be used after a considerable drop had been made, in order to check the descent, would eliminate any question as to the possibility of checking the speed.
The value of the multiple charge rocket for high altitude research is obvious when it is realized that, save for a projectile fired from a gun, which would produce forces too great to be withstood by a delicate apparatus, this method is the only one that does not require the presence of air. Thus the record for airplanes is 6.8 miles, for sounding balloons 21.7 miles, and for pilot balloons (without instruments) 24.3 miles. As is well understood by the United States Weather Bureau, the balloon is limited to but a few miles farther, and if the region above this height is to be explored it must be by rockets of the type that has been described. Already the Bureau has suggested certain recording instruments for the purpose. The writer has called attention to the value of simultaneous observations at the 7-mile level, from stations at considerable distances apart, as a means of obtaining a high altitude weather map for use in weather forecasting and in aviation.
Next, as to the question of propulsion beyond the predominating gravitational influence of the earth, the question that has given rise to most discussion is, perhaps, “What is the value of such performance, even granted that it is physically possible?” This question suggests others: “How are you ever going to recover anything that is sent off in this way?” “How can any ‘volunteer’ (of which there have been 18) return?”
In reply to all these questions, I wish to say first, that I have asked for no volunteers. My only previous signed statement, to the Associated Press, was to the effect that there were very interesting possibilities of the method, but that the work should be put upon a substantial basis before these were discussed. While I realize the absurdity of some of the suggestions when they are viewed in the light of what has so far been published regarding the realization of these suggestions, I wish to say that there are other principles just as fundamental as the multiple charge rocket principle, which I believe can be applied, concerning which experiments have already been performed in some cases, and which I further believe will lead to results of a nature sufficiently sensational to satisfy anyone.
If these matters were not to be kept confidential, at least until the work had been put upon a substantial basis, many who are either not familiar with physical principles, or who do not take the trouble to look into the matter sufficiently, would bring forward all sorts of criticisms, which would result in much talk and little actual accomplishment.
As an illustration of such criticism may be cited the comments made regarding the propulsion of a rocket in a vacuum. Experiments show conclusively that the reaction is even greater at a pressure of one fifteen hundredth normal than at the normal atmospheric pressure, yet when the first announcement of the work was made, surprise was expressed that the Smithsonian Institution could back such an absurd idea as that motion could be produced “by reaction against nothing.”
In the Graphic article Mr. Morrell states that “bodies when they speed through the air are subject to friction against the air which is sufficient to generate tremendous heat” and that “the rocket will generate a red heat for most of the first hundred miles.” This is what would happen if a high speed were maintained throughout this distance, and the air had the same density as at sea level.
As a matter of fact, in the Smithsonian publication in which the experiment is suggested, the velocity is chosen at each part of the path such as to make the mass of the rocket at the start a minimum, taking into account both air resistance and gravity. This velocity must, of necessity, be small where the air is dense, being under 2,000 ft./sec. for the first twenty miles, at which height the pressure becomes but one per cent that at sea level. Even at a 95 mile elevation, the velocity would be but slightly over 2 miles per second, where the air has an estimated density of but four one hundred millionths that at sea level. The speed of 6.4 miles per second, of which Mr. Morrell speaks as causing the rocket to “vanish in an incandescent wisp of flame and smoke” would not be supposed to be reached until an altitude of over 700 miles had been attained, at which height there must exist practically a complete vacuum. The case is entirely different from that of meteors, which enter the earth’s atmosphere with an initial speed of over 8 miles per second.
Concerning next the possibility of striking the moon with a rocket, granting the possibility of attaining that distance, the further comment is made that the earth and moon are moving in different directions at high speeds, the gravitational pull of the earth is complex, and there are unknown air currents. In reply to these criticisms it may be said that although the speeds of the two bodies are high and different they are known, with great precision, at least sufficiently well to make possible the accurate prediction of eclipses, years in advance. Also any “incalculable vagaries of air currents,” above 20 miles, occur in air of practically negligible density.
Further, as the writer has already suggested, there is the obvious possibility, in using the rocket method of propulsion, of correcting the flight by transverse impulses, if necessary, by the aid of photo-sensitive cells, such as the selenium or the thalofide cell, which latter increases greatly in sensitiveness at low temperatures.
In conclusion, not only does the writer believe that the multiple charge rocket principle is correct, as well as the further principles to which allusion has been made, but the experiments so far performed on the small model under test demonstrate clearly the practicability of the idea. This work is proceeding slowly because of the lack of really adequate support, although the Smithsonian Institution is doing as much as it can on a work of this kind. But although there exists the attitude that “everything is impossible until it is done,” there is nevertheless widespread interest being taken in the work. To the writer’s mind, the whole problem is one of the most fascinating in the field of applied physics that could be imagined.
When Body Heat Affects Weighing Operations
There is maintained at St. Cloud, France, the International Bureau of Weights and Measures. And as is quite befitting such a bureau, the methods employed and the apparatus available for the comparison of weights and measures are accurate to a heretofore undreamt of degree. Indeed, in recognition of the work of this institution and particularly of its director, the Nobel Prize for Physics for 1920 has been awarded to M. Charles Edouard Guillaume.
Perhaps none of the features of this remarkable institution is more noteworthy than the precision balances, a description of which is included in the detailed interview with M. Guillaume, which appears in the February issue of the Scientific American Monthly. These precision balances are of great delicacy, nearly all of them being so constructed that they may be read at a distance. Insulated in glass cages supported in piers of masonry which do not touch the floor, they are employed to make comparisons of mass, especially of standard kilogram. One of them, made by Dr. Bunge, is even capable of determining weights in a vacuum.
The day before that fixed on for the experiment the observer places in the cage of the apparatus the weights needed for the next day’s work. He then avoids approaching the balance lest thermic disturbances be produced by the heat of his body. Twenty four hours later, by means of one of the long metal rods which extend from the balance to the observation post, so to speak, he performs the desired weighing operation at a distance of four meters. In other words, the ingenious mechanism at his disposal enables him to place the weights upon the pans, to release the latter, etc., without coming near the scales. He watches the oscillations of the beam of the balance by means of a small telescope. A mirror firmly attached to the balance beam reflects a graduated scale whose movements made when the beam oscillates are seen by the experiment through the telescope.
German Metal Substitutes
A great deal of generalization has been indulged in on this subject, but little of definite statement or concrete detail. Any person in possession of his normal senses must know that Germany had to use other metals in place of copper; and it does not require a great deal of discrimination to infer that the metals which she would use are those which she had. But this is far from telling us just what she did and how she did it, or how her substitutes were made up, or how they stood the test of service. For this purpose the narrative of General Director Albert Wuerth, concluded in the Scientific American Monthly for February, from the January issue, is admirably suited.
Chemistry in Camouflage
When it became necessary to distinguish between different types of green in order that various types of camouflage might be detected in photographs, the solution of the problem ultimately rested with the chemist and the physicist. It was found that so-called uviol and uranium yellow glass, such as had been made by Schott & Company in Jena, would pass a band in the red beyond the visible red and that the green in chlorophyl appeared as red through such a filter. Grass and trees when viewed through such a filter appear red, but green paint continues to appear green. With this as a starting point filters were made finally of sheets of gelatine so stained with a chemical compound as to give the same effect as had been first observed in glass with known chemical compounds.
