These experiments, though they have continued over a considerable period of time, are, unfortunately, by no means conclusive in results. I may as well explain how and why I conducted them. Actual trials of aërial propellers have not very often been made, or perhaps I should say that the results of such trials have not often been published. This latter may be for two reasons : 1st, that inventors wish to keep the results of their investigations to themselves, which, though somewhat selfish, is but natural. 2nd. The results may be such that the experimenters do not think them worth recording. I have considered whether I should not comply with this second reason, and simply look upon the results of my work as negative and not worth recording.

I should like to preface what I am about to say with a word of explanation for the title of the present paper. The title was chosen for me by your much respected Secretary, and I merely acquiesce. The title has a charm for me, realizing how important it is for the elucidation of the many problems held in keeping for us by our atmosphere, that full advantage should be taken of balloon ascents, wherever and whenever opportunity offers, for enhancing our knowledge of the ocean of air at the base of which we live and move. Considering how popular ballooning has been now for more than a century, it is surprising how few of the ascents have been made for really scientific purposes and how few have yielded scientific results.

It has often been supposed that one of the greatest difficulties to be overcome before successful aërial navigation can be achieved is the practical balance of the apparatus in mid-air. Whether or not this will really prove a stumbling-block it is impossible, with our present experience, to state with certainty. Several inventors, it is true, have had considerable difficulties in the initial starting of their machines, which have had a way of toppling over as soon as they have been launched into the air. It seems just possible, however, that if the machine could be properly trimmed before starting, all such difficulties might be overcome. We know that small models, if dropped from the hand or lightly thrown forward, will easily upset, if not properly balanced, but which, if the weights be carefully adjusted beforehand, will fly steadily enough on their downward course.

For general service in aërodynamic experimentation two kinds of anemometer may be useful, one measuring air velocity, the other air pressure. Sometimes the velocity alone is required; again the pressure, either static or impactual, is mainly to be determined.

In either case an accurate and faithful instrument is most desirable. Of course the impact can be calculated from the velocity, and vice versa, providing all the data are at hand for computing the density of the moving fluid. But when many exact determinations have to be made, it is well to evade such calculations by choosing the appropriate anemometer; that is to say, a velocity instrument for measuring velocity, and a pressure instrument for measuring pressure, or impact. One thereby saves much labour, and avoids tho errors that may result from misreading the elements of density.

The soap bubble and the projectile illustrate the two opposite extremes of mechanical flight.

The two greatest hindrances to the solution of this problem have always been the balloon and the screw propeller.

People pick up this and that old device, and fancy that a merely new combination will answer their purpose. The balloon is one such device, having one chief function— that of flotation. Balloon troubles and risks are so well-known to every member of this Society that they need no description. The very obvious schoolboy device of elongating the bulb and driving it end-on with a screw propeller has only resulted in the attainment of a feeble speed, not hitherto exceeding 10 miles an hour in a dead calm.