March 22, 1889.] 



SCIENCE. 



227 



Professor Robinson first considered that the cups moved with one- 

 third the wind-velocity, but this has been repeatedly called in 

 question. In later times the more common method of investiga- 

 tion has been by whirling the anemometer on arms from u to 35 

 feet in length. It would seem as though arms of 1 1 feet could 

 hardly give satisfactory results. 



In discussions of this relation, the utmost confusion has arisen 

 by wrongly considering the so-called "anemometer factor," and by 

 making the same an entirely different quantity, and one from which 

 it was supposed a " friction constant " had been separated. The 

 statement that anemometers used in this country give 20 per cent 

 too great wind-movement has been based on this misconception. 

 Let .r = "anemometer factor," 7c/ = wind-movement, and v ^= 

 travel of the cups : we liave, 



"W 



x = - (I) 



V 



Let a = " friction constant," and i = another constant : we have, 



TU = a + iv (2) 

 Substituting the value of v in (i), we have, 

 iw 



-r = (3) 



w — a 



In experiments at St. Petersburg it was found that an anemometer 

 with 6.72-inch arms and 4-inch cups, the same as used in this 

 country, had i = 2.47, and a = about 2 miles per hour. Assum- 

 ing w at various velocities (5, 10, 15, 20, and 25), we obtain from 

 (3), for x, 4.12, 3.09, 2.85, 2.74, and 2.68 respectively. 



We see that even these earlier investigations show our anemom- 

 eter (with factor 3) almost exactly correct for velocities from 10 

 to 1 5 miles per hour, while at less velocities it gives too little wind, 

 and only about 12 per cent too much at 25 miles. 



The wind records of this country had been so often called in 

 question, the chief signal-officer finally made provision for an in- 

 vestigation of the question. The results in full will shortly be 

 published. For our present purpose it will suffice to give the ap- 

 proximate results with our own anemometer, described above : 

 with K/ at 5, 10, 15, 20, and 25, we obtain for x, 3.30, 3. 11, 3.05, 

 2.98, and 2.89 respectively. These are very satisfactory, and show, 

 that, except for high or low winds, the records are entirely correct. 



It is rather singular that investigations have recently been made 

 in England with a whirling arm of 29 feet, almost the same as that 

 used in this country (28 feet). Unfortunately these experiments 

 were made in the open air, and with a natural wind often 4 miles 

 per hour. These currents vitiated all the results for velocities less 

 than 30 miles per hour : in some cases the error amounted to 35 

 per cent. The helicoidal anemometer which was tested had a 

 vane attached to keep it in the wind. It is of the same nature as 

 the " air-meter," long since discarded for wind measurement, and 

 only used for straight-line currents in mines or elsewhere. For- 

 tunately in these experiments there was one day when it was 

 nearly calm, and the results for that day do not differ from others 

 made in a closed court. For velocities less than 25 miles per hour, 

 these results are entirely unreliable and misleading, in the present 

 state of our knowledge of the problem. An extended discussion of 

 this question will be found in the American Meteorological Joiir- 

 nal for March. 



While much time has been expended on the above problem, yet 

 much more has been spent in determining the relation between the 

 velocity and pressure of the wind. This problem is by far the 

 more difficult to solve, and to practical engineers the more impor- 

 tant of the two. One thing is very gratifying, and that is that the 

 investigations and practice so far have been almost entirely on the 

 safe side ; and the wonder is that buildings havej blown down 

 at all, at least if engineers have ever allowed the commonly ac- 

 cepted figures to enter their computations. It is probable that in 

 most cases engineers have assured themselves of a factor of safety 

 far beyond any thing that any experiments have indicated. How 

 is it that if, as some claim, the usual deductions have indi- 

 cated three times too great pressure of the wind, any building has 

 ever blown down ? If we examine the matter, however, we shall 

 find that most of the theoretical discussions, when separated from 

 well-conducted investigations, will lead and have led far astray. One 



of the most astonishing misapplications has been of Hagen's ex- 

 periments, made with plates from 2 to 6 inches square at velocities 

 from I to 4 miles per hour, to the side of a house 400 inches square^ 

 and with velocities of 60 or 70 miles per hour. But this is not all. 

 Even Hagen's experiments are repudiated by those very persons 

 who make this application, for the reason that they give an increas- 

 ing pressure as the plate grows larger ; so that with a house 400 

 inches square the pressure, according to Hagen's formula, would 

 be seven times as great per square foot as on a plate 4 inches 

 square. Certainly it would be very unscientific to discard the ap- 

 plication of a formula where it does not seem satisfactory, and then 

 apply the computation at another portion of the formula to that 

 portion where we have discarded the same formula. 



The best experiments with low velocities show no increase in 

 pressure per square foot for plates from 4 to 24 inches square ; and 

 when plates have been exposed to the free wind, or at very high 

 velocities, the result has shown 



p == .005 S-dJ- , 



in which/ = pressure, s = surface in square feet, and w = velocity 

 of wind in miles per hour. The recent English experiments were 

 with a plate 6 inches square ; and, even if they were not vitiated 

 by untoward causes, it would be utterly impossible to reason from 

 them to what the pressure would be on a surface four thousand 

 times as great. H. A. Hazen. 



Washington, Marcti i8. 



Queries. 



44. Equilibrium. — In the account of his travels in the Colo- 

 nies, the Marquis de Chastellux relates, that while at Albany, Jan. 

 I, 1782, he was surprised at the noise and racket with which the 

 new year was ushered in ; young folks, servants, and even negroes 

 going from tavern to tavern, singing, and asking for drink. New 

 Year's morning he took leave of Gen. Clinton, and adds, " I met 

 nothing but drunken people in the streets, but what astonished me 

 most was to see them not only walk, but run upon the ice, without 

 falling or making a false step, whilst it was with the utmost dif- 

 ficulty I kept iipo?i my legs" {Travels in North America, 1780-82, 

 London, 1787, p. 441). Here is the best of evidence (for the mar- 

 quis related only that which he saw ; and his narrative, as well as 

 being the most interesting "private " view of our country at that 

 critical period, is also the most trustworthy), asserting that in some 

 way a drunken person, or one not having to the fullest degree what 

 we may call self-control, has a decided advantage over his sup- 

 posed clearer-headed brother, who has refrained from the " flowing 

 bowl." Is this actually the case, or is the advantage more appar- 

 ent than real ? Most of us have at some time noticed the truly 

 wonderful balancings of a drunken person when in pro,Kimity to a 

 curb or flight of stairs, and have commented thereon that a person 

 conscious of the position could not imitate these contortions with- 

 out danger to life and limb. Does extreme mental alertness, then, 

 act as a detriment, while a blunted sensibility is an advantage to 

 the person so conditioned ? If so, the question becomes an impor- 

 tant one, and not confined to conditions of self-imposed disability. 

 We may need to know definitely at certain critical periods whether, 

 in order to accomplish a given object, it is better that we should 

 be partially blindfolded than that we should see and know all. 



A.M. 



Indianapolis, Ind., IMarch 13. 



Answers. 



42. Looking to the Left. — In answer to Query 42, permit 

 me to suggest that seats on the right as one enters a play-house 

 are preferred, because the action on the stage is to the observer's 

 front and left. Troopers, choruses, and principals come on the 

 stage from the left side ; and dialogue, combat, and chief business 

 generally occur in the corner back and to the left ; while the mob, 

 as in Cffisar, and Spartacus the Gladiator, fills in the right. This 

 is the rule in our experience, modified in some cases by the limita- 

 tions imposed by the building. Again, how will " 42 " account for 

 the fact that abroad, confined perhaps to England only, if you turn 

 to the left you are right, while if you turn to the right you are 

 wrong ? L. E. J. 



