Apbil 1, 1887.] 



SCIENCE. 



31T 



few of them," etc. Everybody will imderstand the 

 meaning of the sentence, which was, that a close 

 examination of what he had assumed to be facts 

 might lead to the rejection of a part thereof. 



Bnt it is also perfectly plain that all of this has real- 

 ly no bearing on the point at issue. It is always 

 •easy to quibble about words and phrases, while it is 

 not always easy to avoid error in observation or 

 erroneous deductions from correct observations. 



If Dr. Shufeldt's observations and conclusions are 

 correct, they are of the highest importance, and they 

 mxist be subjected to the most searching examina- 

 tion before acceptance. I must still confess that 

 there is much that is mystei'ious to me in his account 

 of his sensations and observations. I do not under- 

 stand what he means by saying, ' ' My entire system 

 seems to become thoroughly charged with this ani- 

 mal electricity." His "sense of the most profound 

 relief," etc., in the case of the mulatto girl, is a 

 mystery to me. His inability to use any other than 

 a rubber penholder, and the statement that " even 

 then the constant passage of the electricity is exceed- 

 ingly exhausting during most of the time," are hard 

 nuts for me to crack. In short, the whole matter 

 hinges upon the question with which my first letter 

 •closed, — "Is man one of the extremely small num- 

 ber of animals having specialized electrical organs ? " 

 for only in that case is the exj^ression ' animal elec- 

 tricity ' properly applicable. In that letter I gave 

 reasons for the belief that all such phenomena, the 

 «xistence of which was certainly established, were 

 nothing more than cases of accidental electrification 

 by well-known methods and under long-recognized 

 conditions ; that under similar conditions no differ- 

 ences among individuals could exist ; that such 

 electrifications had been known for a long time, 

 and that no extension of well-established principles 

 was needed for their explanation. 



To this statement nothing need be added until 

 Dr. Shufeldt, or some one else, shows that it is in- 

 sufficient to account for observed facts. 



T. C. M. 

 Ten-e Haute, March 27. 



A sensitive wind-vane. 



In the last number of Science, under ' A sensitive 

 wind-vane,' the statement 'The notation is the same 

 as,' etc., should be 'The notation is opposite that,' 

 etc. H. Allen. 



Washington, D.C., March 25. 



As suggested by Mr. Allen in his interesting letter 

 in Science, No. 216, it is important first to determine 

 what is meant by a sensitive vane, and still more im- 

 portant, in my judgment, to determine what kind 

 of a vane is wanted in meteorological observations. 

 I have experimented a good deal with both the long, 

 heavy vanes, and those which are short and light. 

 Neither variety, as ordinarily constructed, is satis- 

 factory. I have more than once seen two large 

 ' standard ' vanes, on the roof of the office of the 

 chief signal officer in Washington, sullenly staring 

 each other in the face, while a very light breeze held 

 a short and very light vane nearly at right angles to 

 both of them. Such performances are confusing, to 

 say the least. But it seems to me not impossible to 

 have one vane which shall satisfy all the require- 

 ments. The desired conditions are to be met with in 

 •what is known as the dead beat galvanometer. In 



this, the needle under the action of a steady current, 

 whether strong or feeble, moves to its proper posi- 

 tion, does not go beyond it, and does not vibrate 

 about it. This is brought about by making use of a 

 force opposing the movement of the needle, which 

 increases with the angular velocity of the needle, 

 and is zero when the needle is at rest. Something 

 of the same kind ought to be accomplished, and I 

 think may be, for the wind-vane. The force oppos- 

 ing the motion of the vane should increase with its 

 velocity, and should be zero when the vane is at rest. 

 If the latter condition is strictly satisfied, it will be 

 infinitely sensitive : the slightest breeze will move it, 

 but the opposing force will prevent violent oscilla- 

 tions. Such a vane will be somewhat slow in its 

 movements, and may not respond to extremely 

 rapid fluctuations in the direction of the wind, 

 through only a few degrees ; but I do not believe 

 meteorologists will consider this a serious objection. 

 What is wanted is a vane which will be steady in a 

 high and somewhat varying wind, and which can be 

 controlled by the slightest movement of the atmos- 

 phere. About two years ago I suggested what ap- 

 peared to me to be a solution of the problem. It was 

 to use a small and extremely light vane, so as to re- 

 duce ordinary friction to the lowest limit, and then 

 to ' deaden ' its motion by means of a liquid damper. 

 This might be applied at the extremity of the axis of 

 the vane produced below the roof, or at any points 

 in that axis. A fan attached to the axis, and mov- 

 ing in a closely fitting vessel of oil or other suitable 

 liquid, would afford almost any desired degree of 

 stability. 



Some steps were taken towards the construction of 

 such a legulator, but I do not think it has ever been 

 completed. Possibly the same method may have 

 been experimented upon by others. T. C. M. 



Terra Haute, March 27. 



A question for economists in regard to value. 



Will not economists undertake to make some agree- 

 ment as to what the meaning of the word ' value ' is 

 to be in scientific discussions? That a uniform 

 meaning be given to this word is most essential to an 

 intelligent discussion of an economic subject. 



As an instance of the necessity of such an under- 

 standing, see the last number of Science ('Professor 

 Marshall on the unit of value '). In that the profes- 

 sor evidently assumes that the market-price of com- 

 modities is their 'value.' Yet we all know that the 

 price of a thing may be greater or less than its 

 ' value' or worth. In order to establish a 'unit of 

 value,' the professor proposes a plan whereby the 

 variations of prices of commodities shall be averaged, 

 and that plan implies that a dollar (money unit) shall 

 be established whose weight shall be increased or de- 

 creased from time to time as the average commodity 

 price increases or decreases. All this is a matter of 

 money and price, and not value. The real thing to 

 be determined is what is value, and then a measure 

 may be designed for it. 



At present there is among economic writers a great 

 confusion in the use of the word 'value.' Some, as 

 Professor Marshall, use it as meaning price (market- 

 price) ; some, comparative utility ; some, exchange 

 value ; some, cost of production in terms of human 

 labor; and some, "the average amount of socially 

 requisite labor measured by time" involved in the 

 production of the article. I hold that this last is the 



