THE CONQUEST . OF THE: AM* IN this small book
of less than two hundred pages the author has concentrated a popular but scientific account of the history of aerial navigation, the principles underlying its accomplishment, a summary of the most recent advances,, and a forecast of its probable future. Professor Botch has been engaged in meteorological research for twenty years past, ,snd for that purpose has founded and maintained an _observatory at Blue Hill, near Boston, ,Massachusetts. He is one , of the highest authorities on the conditions prevailing in. the atmosphere, and was the first to obtain meteorological records by means of instruments carried up to great heights by kites; he has also made many experiments with so-called "sounding" balloons sent up to enormous altitudes._ He has been. closely associated with the chief experimentalists in aerial navigation for many years past, and is familiar with the results obtained with dirigible balloons, "helicopters' aeroplanes, and other .forms of flying-niaehines. Consequently on' both the scientifio and the practical side he is exceptionally well informed, and can speak authoritatively. His book is an excellent example of what can ha done in popularising science when the task is undertaken by an acknowledged -authority, and its general welcome will be ensured by the facts that it _brings information up to April last, and that the statements made are-obtained at first hand from trustworthy sources, , The book is written in popular but exact language, and can • The Conquest of the Air; or, The Advent ef Aerfal Naviratioti.. By I. Laurence Botch, i'rolessor of Meteorology in Harvard Univereity. Now York Moffat, Yard, and Co. L51 net.]
be readily understood by an ordinary reader; it is well produced, fully illustrated, has a good index, and should become a work of reference for all interested in aerial navigation. It contains five chapters. The first deals with atmospheric phenomena, as determined by careful observa- tions in the conduct of which the author has played so prominent a part. The physical characteristics of the "ocean of air" obviously are of first importance in their bearing on aerial navigation. Aeronauts and " aviators " ought to know the varying conditions of pressure, temperature, humidity, wind velocity and direction, occurring at different altitudes, at different periods in the day, and at different seasons of the year. Professor Botch has summarised the known facts in a highly condensed form, and given graphic illustrations; so that readers can readily ascertain for themselves the condi- tions which probably have to be faced when a voyage through the air is undertaken. He has also indicated the bearing of the most important of these phenomena upon the dangers incidental to aerial navigation, the possibility of directing ordinary balloons on any desired course, the designing of dirigible balloons, and the precautions necessary in designing and operating flying-machines. Some idea of the range over which observations have been carried will be obtained from the statement that " sounding " balloons have been sent up to a height of eighteen miles, which Professor Botch considers to be "more than twice as high as a human being can hope to attain." In his judgment, aerial navigation will be carried on at heights not exceeding one to two miles, and within this range of altitude detailed information is given for variations in temperature, pressure, humidity, and wind velocities. This chapter, while complete and thorough, is not "out of scale" when compared with those which succeed it, Professor Botch having avoided the pitfall into which many men of science stumble when dealing with their particular subjects.
The " History of Aerostation " forms the second chapter, and outlines the narrative from the fourth century B.C. up to the present use of ordinary balloons for purposes of sport, exploration, and military reconnaissance. Probably the most interesting section is that in which Benjamin Franklin's letters of 1783 to Sir Joseph Banks—describing the ascents made by the brothers Montgolfier and other French balloonists—are reprinted. Franklin's comments on the possible uses of balloons for aerial navigation are still worth attention.
In the third and fourth chapters dirigible balloons and flying-machines are described and discussed, and these chapters contain what is probably the best and most trust- worthy short summary available at present of details of design and actual performances for successful inventions. The scientific principles of aerial navigation are laid down ; the difficulties to be overcome in securing stability, in varying heights, in meeting changed conditions of wind pressure and Airection, and other matters of primary importance, are dealt with briefly but clearly. The work of men who have largely influenced progress is described: including that of Langley, Charente, and the Wright. in the -United States ; of Santos-Dumont, Renard, and others in France ; of Zeppelin, Gross, and Parseval in Germany. British work in this direction compares unfavourably up to date with that done abroad, and receives little notice from Professor Botch. It may be hoped, however, that the systematic efforts now being made, with Government support, will speedily enable our position to be retrieved. One important aid to this result will clearly be the utilisation of valuable experience acquired else- where by men—like the Wright. and some French inventors— who are free to sell. on terms to be arranged, the knowledge gained by long-continued experiments. A similar course was taken by the Admiralty in regard to submarines,—the right to use the patents of Mr. Holland (an American) was pur_ chased, and in the bands of competent British engineers lost ground was rapidly recovered, and a lead ultimately established."
The final chapter deals with " The Future of Aerial Navigation," and contains not only the views of the author, but those of other recognised authorities. Abridgment or summary of this section is practically impossible ; the book itself must be read in order that the conclusions may be mastered. Certain salient points may be mentioned. Recent progress in aerial navigation is shown to be based chiefly on improvements in internal-combustion engines, enabling
greater power to be developed for a given weight of machine, Further advance in this direction is necessary, and it is essential to success that propelling machinery shall be trust- worthy and durable as well as light. The use of dirigible (or motor) balloons a.. agents in warfare is discussed, and the serious view of the matter taken by France and Germany is illustrated by the statement that the former country spent £56,000 and the latter £134,000 in experiments on aerial machines during the year 1908. For certain purposes—such as reconnoitring—dirigible balloons are considered to be of service ; it is thought also that they might carry and drop explosives ; but the number and weight of such projectiles would be limited, and the rebound of the balloon after a dis- charge would require to be controlled. Professor Botch thinks that the dirigible balloon has probably nearly reached the limits of development, and that it will not come into general use on account of the cost of construction, operation, and maintenance. His verdict in regard to flying-machines is that at present, with " their uncertain motors, defective methods of launching, and unstable equilibrium," they cannot be applied to offensive military purposes. Another notable conclusion is "that neither class of aerial craft will ever compete with railroads or ships as commercial travellers." Here we must conclude ; as was said above, the book itself must be read in order to appreciate its value fully.
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