THE VELOCITY OF THE WILL. 361 



headquarters of the will. Here is one second lost. What takes place 

 then ? How much time does reflection need ? That depends on cir- 

 cumstances ; but it is certain that the will does require a measurable 

 time to make a decision. Then it acts ; the order is sent out to the 

 tail to thrash the boat to bits. Another second elapses before the 

 message reaches its destination: total, two seconds gone, during which 

 the boat and sailors get off clear by vigorous rowing. 



It will be asked, How have philosophers succeeded in measuring the 

 rapidity of the onward movement of nervous stimulus ? Several meth- 

 ods of calculating it have been devised. A doctor of the middle ages, 

 cited by Haller, gave some thought to it long ago. He conceived a 

 singular notion that the speed of the nervous fluid might be de- 

 duced from that of the blood in the aorta ; these two rates, he fancied, 

 must be in the inverse ratio of the sizes of the aorta and the nerve- 

 tubes. That calculation assigned, as the speed of the nervous fluid, 

 600,000,000,000 of yards a minute 600 times the rapidity of the 

 motion of light. 



Haller himself undertook the task in a different way. Reading 

 the " iEneid " aloud, he counted the number of letters he could pro- 

 nounce in a minute with a very rapid utterance. He found 1,500 

 the extreme limit, or one fifteen-hundredth part of a minute for each 

 letter. Now the letter r requires, Haller says, ten successive contrac- 

 tions of the muscle that gives the tongue vibration, and from that, he 

 adds, we may conclude that in one minute this muscle can contract 

 and relax 15,000 times, which represents 30,000 simple motions. The 

 distance from the brain to the muscle in question is a little over three 

 inches. If the nervous fluid travels it 30,000 times, that makes more 

 than 9,000 feet, and 9,000 feet a minute represents a speed of 154 feet 

 in a second. This reasoning is a mere sequence of mistakes, and the 

 approximation to the right view that Haller gained is the more aston- 

 ishing because his method was not in the least likely to ascertain it. 

 The "iEneid" justifies, in this instance, its ancient pretensions as a 

 book of oracles. 



Not until 1850 were these researches resumed by a new method 

 that led to the solution of the problem. It is due to Helmholtz, the 

 most famous of the German physiologists, who unites, to rare talent as 

 an observer, the profound learning of a consummate mathematician. 

 His first method is founded on the use of the chronoscope of Pouillet. 

 A galvanic current of very brief duration acts at a distance on a mag- 

 netized needle, and swings it away from the normal position ; the 

 range of the deviation is measured, and the length of the current de- 

 duced thence by calculation. A means is thus gained for measuring 

 intervals of time not exceeding a few thousandths of a second. Helm- 

 holtz applied this method in the following way : One of the muscles 

 of a frog's leg is fixed at one extremity in a nip, and attached at the 

 other extremity to a little lever forming part of a galvanic circuit. A 



