588 ANNUAL, REPORT SMITHSONIAN INSTITUTION, 19 3 8 



terminal delays need to be taken into account. It appears that when 

 a nerve impulse starts from, say, the hand to reach the brain, the over- 

 all time taken for the response is very much longer than that of the 

 mere passage of the signal along the nerves. This time lag before 

 the brain is able to act on information received was, I feel sure, an 

 important factor in some tests carried out a number of years ago at 

 Farnborough. It was then thought that it would be a good thing 

 if an indication could be given to the pilot when he pulled out from a 

 dive, of the moment when he put on an acceleration higher than was 

 safe. This indication was given by having inside the control lever 

 a tiny accelerometer unit which, when the acceleration passed any 

 set limit, say, 4 g., jerked the pilot's hand. The jerk warned him that 

 it was advisable to slacken off the rate at which he was pulling out. 

 The instrument worked well, but the idea failed because although the 

 indication was given to the pilot's hand and thence to his brain, the 

 airplane was too quick for the combination. Careful laboratory 

 tests showed that it was impossible for the pilot to push the control 

 lever forward in less than one-fifth of a second after the indication 

 had been given by this device to his hand. In actual flight the time 

 lag might be longer. In the words of the report 6 presented to the 

 aeronautical research committee: "In the case of intentionally violent 

 use of the controls no warning however swiftly given could be of serv- 

 ice to the pilot." 



Incidentally, anyone who wonders what an acceleration of 5 g. is 

 like can obtain the information without getting into an airplane at all. 

 Consider a child swinging in an ordinary garden swing. If the child 

 swings up to such a height that he can just see the horizon over the 

 top bar he will experience as he rushes past the bottom of the swing 

 an acceleration force of 3 g. If the swing be of the fair type with 

 iron rods in place of ropes we can in theory, at any rate, start the 

 swing from the very top (so that the poor child is inverted and has to 

 be strapped in). In this extreme case the acceleration force when the 

 seat swings through its lowest position will be exactly 5 g.; and this 

 it will always be whatever the height of the swing or the weight of the 

 child. 



The effect of applying to the human body a steady lateral acceler- 

 ation can also be illustrated by an ingenious device at the University 

 of Gottingen, where a cylindrical room is mounted on bearings so 

 that it may be rapidly rotated. People standing in that room see 

 nothing but a dial to tell them that the room is being rapidly turned 

 round, but the effect upon their limbs when they try to use them, 

 and still more on their mental sensations when they suddenly incline 

 their head serves to show how easy it is to deceive the brain as to what 



* R. & M. 1446. 



