April 10, 1885.] 



SCIENCE. 



295 



muni height above the plane which passes through 

 the upper edges of the orbits and the orifices of the 

 ears. Mr. Galton adds, that while writing his ac- 

 count, instruments for head measurements were 

 being solidly constructed for him, which will be in 

 use in Cambridge, Eng., in 1885. 



THE STA TUS OF AERONA UTICS IN I884. 



Duboy de Bruigxac, member of the French 

 Society des ingenieurs civils, has recently presented 

 to that association a very complete yet concise 

 expose of the present state of the art of aeronautics, 

 especially as related to the general system of ' dirige- 

 able ' aerostats. The first indications of success are 

 assumed to have been given by the experiments of 

 Giffard (1852-55), Dupuy de Lome (1871), and Tis- 

 sandier and Renard and Krebs (recently). The first 

 condition is considered to be stability, retaining the 

 relative position of parts seen in the earlier balloons. 



Giffard, in his earliest attempts, attained a speed 

 of three, and later of four, metres per second. 

 Dupuy de Lome, and Renard and Krebs, have used 

 better forms of balloon, and have secured more 

 rigidity of structure: but none have obtained high 

 speed. 



Extreme lightness of motor is a vitally essential 

 feature ; and the best that has yet been done is 

 illustrated by the steam-engines of Thorneycroft, 

 weighing about 33 kilograms (73 pounds) per horse- 

 power, and which, by sacrificing economy of fuel, 

 it is thought possible may be reduced to 20 kilos 

 (44 pounds), and the various storage and other bat- 

 teries yielding electricity, which, according to Tissan- 

 dier, may be reduced to a weight not exceeding 25 

 kilos (55 pounds) per horse-power. Messrs. Renard 

 and Krebs claim a weight as low as 17 or 19 kilos. 

 The experiment of Tissandier in 1883, in the appli- 

 cation of electricity to this work, is thus expected to 

 lead to useful results. 



The propelling instrument is always the screw. 

 Its position is a matter of importance. As usually 

 arranged, it has a tendency to cause vertical devia- 

 tions of the machine, which are objectionable. It 

 is hoped that it may prove possible to place the 

 screw-shaft in line with the axis of symmetry of the 

 balloon, in order to avoid this difficulty. This may 

 be done by setting it between a pair of spindle- 

 shaped supporting balloons. It is uncertain whether 

 it will be found best to place it ahead or astern of 

 the balloon; but it is presumed best at the stern. 

 The screw is objectionable on the score of its low 

 efficiency, — about 0.30 (?); but nothing better has 

 yet been devised. 



Bruignac proposes a formula by means of which 

 to calculate the resistance of the aerostat, and by 

 its application determines the relative resistances of 

 the machines of the several aeronauts whose work 

 has been mentioned, as follows: Giffard, 1852, 0.076; 

 Giffard. 1855, 0.035; Dupuy de Lome, 0.18; Tissan- 

 dier, 0.12; Renard and Krebs (1), 0.12; Menard and 

 Krebs (2), 0.02. In the last two cases, the large and 



the small ends of the vessel are calculated sepa- 

 rately. 



The speeds actually obtained by them were 5.5 

 metres per second by the last named, and from 3 to 4 

 metres by their predecessors. Had the former driven 

 their machines with the small end ahead, instead of 

 the larger end, as actually practised, the critic calcu- 

 lates that they might have obtained a speed of nearly 

 ten metres. A symmetrically formed cylindrical 

 spindle is advised as the probably best form for the 

 body of the air-ship, inserting a straight middle 

 body when constructing very large vessels. The 

 larger the machine, the lighter, comparatively, will 

 be the driving machinery. The substitution of sup- 

 porting hoods, sheets, or tissues, for cords, may assist 

 in the endeavor to reduce resistances. The loss of 

 gas by leakage can be reduced by choice of proper 

 material for the balloon. The waste of gas in ascend- 

 ing and descending must be avoided, and may, per- 

 haps, be obviated altogether. This becomes an easier 

 matter in ascents of the kind here contemplated, in 

 which no greater height will be sought than is suffi- 

 cient to clear obstacles safely: probably a hundred 

 metres will prove ample. For such work, the alter- 

 nate compression and expansion of the adjusting 

 volume of gas will probably suffice. 



The conclusion is reached that the art of aerosta- 

 tion is much nearer a practically applicable state 

 than scientific men generally suppose. The objects 

 now sought are the attainment of better and more 

 stable forms, the more effective arrangement of parts, 

 the invention of lighter motors, invariable in weight, 

 and convenient of operation, and the securing of 

 higher efficiency of propelling instrument. Even 

 now, with the experience of the past, it is possible to 

 build a machine of this class capable of making at 

 least ten metres per second through the surrounding 

 medium. 



These conclusions of Bruignac are especially in- 

 teresting when compared with those of Pole as 

 presented to the British institution of civil engi- 

 neers, in which he finds that the supporting-power 

 of the balloons adopted by the aeronauts above men- 

 tioned, and the driving-power and weights of the 

 torpedo-boat engines of British makers, are such as 

 should permit the construction of an air-ship four 

 hundred feet long, to travel at the rate of thirty 

 miles an hour. R. H. Thurstox. 



FINDING A BORE-HOLE. 



Two novel and ingenious methods of locating the 

 position of a bore-hole have recently been described 

 in the London Engineering. In the first case, at 

 Edinburgh, it was desired to connect the lower end 

 of a bore-hole, two hundred feet deep, with a well 

 some eighteen feet distant. A drift run in the sup- 

 posed direction failed to strike the hole, although 

 much rock was cut away, and it was evident that 

 the drill had deviated considerably from the vertical. 

 After an unsuccessful attempt to locate its direction 



