Meteorology. — "An instrument to he used hy the pilot of an 

 (leroplme to measure the vertical velocity of the machiiu' . 

 Bj Dr. C. ScHOUTF, F. A. van Heyst, and N. E. Orokneveld 

 Meyek. (Conimiinirated by Dr. van dkr Stok). 



(Communicated in the meeting of June 29, 1918). 



In many cases it is impcuMant that the pilot of an aeroplane 

 should get direct information about the velocity of climbing or 

 falling of his machine, and in the greater part of these cases it is 

 of a higher value that he should know the vertical speed with 

 respect to the medium, the air, than in relation to the earth. The 

 latter especially when he wishes to know the velocity of ascent or 

 descent to be able to judge the effect of his altitude-steerage, as well 

 in relation to the safety of flight as where either an extreme quickness 

 or an extreme slowness of the climi)ing or falling is required. 



As a rule the vertical speed is determined by measuring the 

 quickness with which the atmospheric pressure varies. Therefore 

 baromeliic readings can be executed after certain intervals, in that 

 case however we do not get instantaneous values. The quickness of 

 the changes in the pressure of the air can also be measured by 

 means of the so called variometer, consisting of a vessel that com- 

 municates with the outer air by a narrow opening or a capillary 

 tube and is provided vvitii another tube in which a liquid-column 

 can move to and fro wlien notwithstanding the "leakage" an under- 

 pressure or an over-pressure is generated in the vessel. All these 

 determinations based on pressure-changes give the vertical speed 

 in relation to the earth and not to the medium, and moreover the 

 results are not independent of the height at which they are 

 obtained; so that generally a correction, and often a considerable 

 correction, has to be applied. 



This complication does not arise when the determination is made 

 by vertical cup-anemometers. The idea suggests itself, to get indications 

 of the vertical speed electrically hy means of a dynamo-armature 

 mounted on the axis of a xertical anemometer. The more so because 

 indications at a distance ai-e wanted, as the anemometer requires 

 to be mounted in undisturbed air, which as a rule is not to be 

 expected immediately in front of the pilot-seat. In such measurings 

 however, the result would be spoiled by the friction, which is un- 

 avoidable in the anemometer, and which cannot be slight in this 



