no necessity to analyze it in detail. We will simply remember that a rapid air-ship is necessarily stable.

IV.

From the foregoing the conclusion may be drawn that the different qualities which an air-ship may possess are not independent of each other but may be reduced to two fundamental properties, the individual velocity and the carrying capacity. The first of these qualities, the individual velocity, is highly desirable in itself, for without it dirigibility is impossible. Furthermore, it is the only means by which we can increase the absolute velocity, which is of such practical importance. Finally, the absolute velocity is one of the factors determining the distance that can be covered in a single flight. When the individual velocity is increased, for the same reason both the absolute velocity and the distance covered are increased. If we also add the consideration that the possession of this speed necessarily implies the possession of stability in all directions, we must conclude that in it we have a quality that is essentially fundamental.

The carrying capacity of such a machine can be measured by the amount of weight of every kind which it can carry in excess of the weight of the air-ship proper, its motor, propellers, and all the parts indispensable to its operation.

Given this weight it can be used in different ways. It can be employed in transporting a number of passengers or a considerable weight of merchandise. In the form of ballast it helps to attain the greatest altitude, and thus contributes to the duration of the aerial voyage. In the form of fuel supply it assures the duration of the voyage, thus affecting one of the two factors entering into distance covered.

Individual velocity can not be present in a high degree if the property of stability is not also present. This permits of the attainment of an absolute velocity which, coupled with duration of voyage, goes to make up distance traveled. The carrying capacity has no relation to stability. It can be utilized either for its own sake or to attain altitude, or to prolong the voyage and thus contribute in increasing the distance traveled.

These different qualities may therefore be divided into two groups, those dependent on the individual velocity and those on the carrying capacity. As for the distance traveled, it is a common resultant of the two groups, for it is the product of absolute velocity by duration of flight, qualities belonging to the different groups.

If we wish to obtain a synthetic idea of the value of an air-ship, it is by the ratio of the distances covered that their merit should be measured, but this quality is only the product of two others—the

absolute velocity and the duration of the voyage. These two factors may play a varying rôle in the final result.

The factor of duration is certainly less important than the velocity. To obtain duration the machine need not even be dirigible; a simple free balloon can possess this quality, while up to the present time it is the spherical balloons which have made the longest uninterrupted voyages, so that while recognizing the valuable index which the distance traveled affords in the estimation of the merit of an airship, still, of the two elements which go to make it up, we must attach more importance to the absolute velocity than to the duration of flight.

It should be recalled, however, that these two qualities are not fundamental. The absolute velocity itself depends on the wind and the individual velocity, and from our point of view it is only important if it is attained by the caprice of the wind but in the direction desired by the pilot. To accomplish this, there must be individual velocity, a fundamental property.

The duration of flight is itself dependent on the carrying capacity. We must, therefore, conclude that of these two fundamental properties it is the individual velocity that stands first and the capacity of transport takes second place.

As stated in the beginning of this discussion, I have arrived at these conclusions simply from utilitarian considerations. If we examine the question from the point of view of the difficulties to be overcome, what rank shall we assign to these two essential qualities of an air-ship? For an aeroplane the question is very simple; the difficulties are the same in acquiring one as in acquiring the other. With an increase in the individual velocity, the possible load per square meter of sustaining surface is increased. Consequently, in making an advance in one a gain is made in the other. The question can be summed up by saying that an aeroplane should be as perfect as possible; that is, it should be stable, have carrying surfaces endowed with the best sustaining qualities, a good propeller, and a powerful and light motor. If it possesses such perfection it can be used in any way desired; it can travel swiftly and yet carry a considerable weight that may be utilized either as useful load or to increase the duration of the flight. If its load is lightened its speed will be diminished, but its abundant motive power will enable it to ascend. To conclude, with a perfect aeroplane the aviator may obtain whichever quality he desires or combine them in whatever proportion he deems convenient.

In the case of aeroplanes, therefore, we may say that the question of difficulties to be overcome is negligible, and that utilitarian considerations alone determine their value. In these machines it is the individual velocity, as it is in all other types, which is the most im

portant quality, but the others can be obtained without modifying the construction in the slightest degree, and except for attaining altitude, without losing any velocity, but even gaining it, with an increase in the carrying capacity and in the qualities which are dependent on it. This is not the case with dirigibles. To be sure, with them as with aeroplanes, general perfection of apparatus-motor, propellers, forms of small resistance-is indispensable to velocity and can likewise exert a favorable influence on the carrying capacity and its resulting consequences, but another factor intervenes, the volume of the balloon. This exerts an enormous influence on the carrying capacity, which dwarfs that resulting from the general perfection of the apparatus. Although by increasing the individual velocity we can indirectly increase in a slight degree the carrying capacity, we possess, moreover, a means of increasing this quality absolutely independent of those which produce velocity. I may add that this method has no great merit in its application. It is not very difficult to add a few hundred cubic meters to a balloon, or even more. I would not go as far as to say that the problem is of extreme simplicity, but it is a small matter beside those that have to be solved in increasing the individual velocity of a dirigible. Consequently, as far as machines lighter than air are concerned, if from a utilitarian point of view the carrying capacity is an inferior quality, it is equally so from a technical standpoint, for it is much easier to attain than individual velocity.

Thus there are in an air-ship only two fundamental qualities from which all the others are derived, individual velocity and carrying capacity; and from a practical standpoint the latter is much less important than the former.

In considering the difficulties to be overcome, in an aeroplane the question does not arise, for in such apparatus the qualities sought for are so involved one with the other that every added improvement allows of the increase according to choice of one or the other of the properties desired in an air-ship. With dirigibles this is not the case, for carrying capacity is much more easily obtained than individual velocity, and the technical considerations which are involved in machines lighter than air are merely those that are basic in the utilization of an air-ship.

Simply because a colossal dirigible has accomplished long journeys and covered great distances, the superiority of this type of air-ship over all others should not necessarily be proclaimed. The machine that should interest us most is the one capable of the greatest individual velocity, and as this velocity is difficult to measure, we should estimate it from the absolute velocity attained in flying in a closed circuit in such a way as to eliminate from the final result, as much as possible, the effect of the wind.

I believe that in this respect our air-ships have nothing to envy in those of foreigners. I even believe frankly that ours are superior. We can continue to be proud, then, of our air-ships; they possess to a higher degree than others the first of all qualities, individual velocity. They are gaining in this respect from day to day, and when our engineers desire it they can provide them besides with the carrying capacity of which our rivals are so proud.

France is in no danger, as has been frequently loudly announced, of losing the empire of the air.

These lines were written before the catastrophe of the dirigible Republique. This tragic event, nevertheless, does not alter the conclusions of this article in the slightest degree.-RENARD.

RESEARCHES IN RADIOTELEGRAPHY."

(With 2 plates.)

By Prof. J. A. FLEMING, M. A., D. Sc., F. R. S.

Radiotelegraphy, popularly called wireless telegraphy, has outlived the tentative achievements of its precocious infancy and obtained for itself a settled but important position amongst our means of communication.

This stage, however, has only been reached after a long struggle with experimental difficulties and much labor in analyzing the processes involved. As many of these matters are of general scientific interest, it is proposed, during the present hour, briefly to summarize the results of some recent research.

You are doubtless all aware that every radiotelegraphic station comprises three elements. There is, first, the external organ called the air wire or antenna, by which the electromagnetic waves are radiated and absorbed. This antenna consists of one or more wires extending up into the air, either vertically or sloping, or partly vertical and partly horizontal. These wires are insulated at the upper ends and may be arranged fan fashion, or may form one or more nearly closed loops, placed in a vertical position. The antenna is, so to speak, the mouth or ear of the station, by which it speaks through the ether, or by which it hears the etherial whispers coming to it from other stations. The ether waves are produced by very rapid electric currents moving to and fro in the antenna wires, and these, like the vibrations of a violin string, or the aerial oscillations in an organ pipe, set up a periodic disturbance in the surrounding medium, which in the electrical case consists of alternating electric and magnetic forces taking place at each point in space around the antenna.

There are, then, appliances in the station collectively called the transmitter, which have for their function to create these powerful electric oscillations in the antenna, and to control them so as to send out short or long trains of ether waves in accordance with the dot or dash signals of the Morse alphabet. Lastly, there is the receiving

Lecture before the Royal Institution of Great Britain, Friday, June 4, 1909. Reprinted by permission from pamphlet copy published by the Royal Institution.