INDUSTRIAL PKOGKESS DURING THE YEAR 1876. xlix 



by which the speed of a vessel at any given instant may be ascer- 

 tained by inspection. It consists of two corrugated circular boxes 

 like those used in aneroid barometers, but not exhausted, the one 

 side of each of which communicates with a tube passing into the wa- 

 ter. These two tubes are bent at right angles at their lower ends, and 

 face opposite ways. The inside faces of the boxes are connected by 

 means of a rod having rack-work upon it, into which gears a pinion 

 upon the arbor of an index hand. Should the pressure in one box 

 be different from that in the other, the rod would move, and the in- 

 dex too. But whatever the absolute variation of pressure, provided 

 it is the same in both boxes, no effect is produced on the dial. By 

 means of connecting tubes and an aspirator, the wdiole apparatus is 

 filled with water. Then it is unaffected by the vessel's pitching 

 and tossing, and indicates only the speed with which she passes 

 through the water. By simple means it may be made self-record- 

 ing, 



Romilly has studied the action of a current of air or steam in 

 drawing into its course the surrounding air, using for this purpose 

 various forms of openings and ajutages. The same results were ob- 

 tained with air and steam, the maximum pressure in the receiver be- 

 ing obtained wdien the receiving cone has an angle of 5 to 7, the 

 base directed away from the jet. This latter is placed at a distance 

 from it determined by making the jet the apex, and the opening of 

 the receiving tube the base of a cone of 15. TJien the quantity of 

 air drawn in is directly as the diameter of the two openings (of the 

 jet and receiving cone) ; the velocity is in the inverse ratio ; the 

 pressure is inversely as the section of the receiving tube, the abso- 

 lute pressure varying according as the receiver is opened or closed. 

 He has also observed that, using a receiver with thin walls, if the 

 jet be removed only a few millimeters from it, and directed not into 

 the opening of this receiver, but just outside of it, and upon the wall 

 itself, a maximum of pressure is produced more than double of that 

 obtained when the jet enters the orifice. Using a jet provided, like 

 the receiver, with lateral w^alls, there is no longer a pressure, but an 

 aspiration produced, even at considerable distances. 



Penaud has presented to the French Academy an important mem- 

 oir on aviation, in which he describes his new apparatuses for me- 

 chanical flight. He divides the systems of aviation already proposed 

 into three classes : helicopters, aeroplanes, and orthopters. In the 

 first, screw-propellers with nearly vertical axes constitute the sus- 

 taining power ; in the second, the surfaces are nearly plane, inclined 

 slightly to the horizon, and the apparatus is propelled by screws ; 

 the third are furnished with organs whose surfaces have nearly ver- 

 tical and alternating movements. In 1870 one variety of helicopters 

 was constructed which would rise to a height of fifteen meters, and 

 remain in the air for twenty seconds. In 1871 an aeroplane was 



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