April 22, 1909] 



NA TURE 



and it was not the mathematician who detected 

 its error, in fact we have plenty of mathemati- 

 cians to-day who can prove by formulce that 

 Newton's law is absokitely correct and unassailable. 

 ..." his information does not agree with the facts of 

 the case. What about Kirchhoff's theory of discon- 

 tinuous fluid motion, to mention nothing else? 



.\gain, it is rather amusing to see mathematicians 

 accused of demonstrating " by formulse, unsupported 

 by facts, that there is a considerable amount of skin- 

 friction to be considered," when the usual complaint 

 is that they will assume all their bodies to be per- 

 fectly smooth, and will not take account of frictional 

 resistances in solving their problems. But some clue 

 as to where Sir Hiram finds his mathematicians is 

 afforded by his reference (preface, p. x) to a recent 

 controversy in Engineering. Surely he cannot sup- 

 pose that the authors of difficult mathematical re- 

 searches would, as a rule, publish their best work in 

 journals devoted to the interests of practical engineers, 

 even if the editors would consent to print them! If 

 he would consult the pages of journals and transac- 

 tions devoted to researches in mathematics and 

 mathematical physics, he would soon discover the 

 paucity of papers to which Prof. Chatley refers. 



On pp. 104 to 108 he publishes figures of stream- 

 lines taken (so be says) from " mathematical " 

 treatises, and all he is able to say is that " just how 

 or why " the air moves in these particular ways is 

 not evident. Now, in the first place, the diagrams 

 show complex systems of eddies, the equations of 

 motion of which no mathematician would ever 

 attempt to integrate, and in the second place the 

 question is not how the air is likely to move, but how 

 it actually does move? 



As an exponent of experimental versus mathe- 

 matical methods, why did not Sir Hiram put the 

 matter to a decisive and conclusive test by deter- 

 mining experimentally the form of the stream-lines 

 produced in the neighbourhood of the various sur- 

 faces shown in these illustrations? Experimental, 

 and in particular photographic, methods of plotting 

 stream-lines are not difficult, and they can be con- 

 ducted at a very trifling expense. Some of those who 

 are, or have been, conducting such experiments are 

 not altogether uninathematical in their methods. 

 Surely Sir Hiram Maxim has missed a grand oppor- 

 tunity of scoring off his " mathematicians." 



It was in 1894 that the author's gigantic experi- 

 mental machine ran to and fro between rails. To 

 all that has been done since that time onlv about 

 five pages, including illustrations, are devoted in a 

 chapter on " Some Recent Machines," and an equal 

 number in a chapter headed "Balloons"; and yet 

 the fifteen years that have just elapsed form the most 

 eventful period in the whole history of artificial flight. 

 It is the experimenters who have expended time and 

 money, and have even sacrificed their lives, rather 

 than the mathematicians, who have cause for disap- 

 pointment at the scanty recognition they have 

 received. 



.An address on " Recent Progress in .Aeronautics," 

 delivered before the engineering' section of the 

 American .Association at Baltimore by Major George 

 O. Squier, is published in Science for February ig. 

 It is in the nature of a general summary, and deals 

 both with balloons and aiiroplnnes, but the treatment 

 of resistances on " arched surfaces " reveals an im- 

 portant gap in the experimental information dealt 

 with in the address. It is tacitly assumed that the 

 only effect of arching the surface is to increase the 

 coefficient of resistance, the angle of flight being 

 taken " to be the inclination of the chord of the sur- 

 face to the line of translation." This would be all 



NO. 2060, VOL. 80] 



right if we were sure that the resultant reaction was 

 always perpendicular to the chord, but it is pretty 

 certain that such is not the case. If the aerocurve 

 forms a circular arc, the resultant must (in the 

 absence of skin-friction) pass through the centre of 

 curvature, and if the centre of pressure is in front 

 of the centre of the arc, the effective angle of flight 

 will be less than the inclination of the chord, that is, 

 the ratio of drift to lift will be less than the tangent 

 of the inclination of the chord. Experimental in- 

 formation on this point is very scanty as a rule, a 

 notable e.xception being Mr. TurnbuU's investigations 

 of plane, concave, convex, and doubly curved surfaces. 

 .Again, e.xception may be taken to the statement that 

 " the helicopter type of machine may be considered as 

 the limit of the aeroplane when by constantly increas- 

 ing the speed the area of the supporting surfaces is 

 continuously reduced until it practically disappears." 



In his suggestions for " the stabilisation of aero- 

 planes " in La Revue des Idces (Paris, February 

 15), M. Etienne Maigre deals with lateral stability, 

 and assumes that the lateral balance is to be main- 

 tained, not automatically, but by the voluntary or 

 involuntary effort of the aviator. He suggests the 

 use of two triangular surfaces attached to the main 

 aijroplane and controlled by hand. He assumes Otto 

 G. Luyties' law, according to which the normal 

 resistance varies as 2 sin «- sin-' a, and finds a maxi- 

 mum lift for an angle of 37°. 



Captain Renard has been giving a series of con- 

 ferences before the Soci(-t^ d' Encouragement pour 

 1 'Industrie national, of which the first has ap- 

 peared in the Bulleiin (Paris, January). Captain 

 Renard distinguishes six different methods of experi- 

 menting on air-resistance, including the use of ex- 

 periments in water, with suitable allowances for 

 difference of density. The need of further experi- 

 ments in this direction is strongly emphasised. 



It is to be noticed that the art of designing gigantic 

 airships fitted with saloons, cabins, and mess-rooms 

 has not yet faded away into past history, despite the 

 recent advances in aeroplanes and dirigibles. About 

 the beginning of February the Standard devoted more 

 than half a column to an American project very sug- 

 gestive of the Minerva of Robertson or the gigantic 

 apparatus for which M. Petin raised loool. in the 

 early days of ballooning, but for which the gas supply 

 proved inadequate. G. H. Bryan. 



DEW-PONDS. 



A GROWING interest in the subject of dew-ponds 

 has been exhibited in recent years, but it has 

 yet to be proved whether there is actually such a 

 thing as a true dew-pond. Dew-and-mist ponds there 

 undoubtedly are, but dew and mist, similar in essence 

 as they may be, are yet distinct and separate meteor- 

 ological phenomena. The term " dew-pond " has 

 arisen from the careless habit of assuming that every 

 form of condensation of aqueous vapour which is not 

 seen as rain or snow must be called dew. 



The Journal of the Society of .Arts (March 5) con- 

 tains a paper on the subject by Mr. Geo. Hubbard, 

 and he has therein endeavoured to show how artificial 

 deposition of dew may be brought about in a pond. 

 He maintains that by laying down a bed of straw 

 beneath puddled clay, the water may be chilled suffi- 

 ciently to cause the atmosphere to give out aqueous 

 vapour as dew. In his earlier remarks on the subject, 

 it was the chilling of the puddled clay to which he 

 attributed deposit of dew. Of course, if a pond were 

 fairly full there would be but little puddled clay ex- 

 posed, so now he attributes the additional supply to 



