SCIENCE. 



[Vol. XIII. No. 312 



the Lowell Institute, Boston, in 1889, devoted to Alexander, Han- 

 nibal, Cassar, Gustavus Adolphus, Frederick, Napoleon, and the 

 record of their achievements and the analysis of what each of them 

 contributed to military science ; " Ancient and Modern Light- 

 Houses," by Major D. P. Heap, Corps of Engineers, U.S.A. ; anew 

 ■edition of "Discourses on Architecture," by E.-E. VioUet-Le-Duc, 

 Tichly and copiously illustrated with hundreds of steel engravings 

 and woodcuts, translated from the French by Benjamin Bucknall ; 

 a new and cheaper edition of " A Hand-Book of Christian Symbols 

 and Stories of the Saints, as illustrated in Art," by Clara Erskine 

 ■Clement and Katherine E. Conway ; and " His Two Wives," a 

 novel, by Mary Clemmer, being No. 50 of Ticknor's Paper Series. 



LETTERS TO THE EDITOR. 



■ible. The 





nication -ivill he /itrnished 



"* ^Correspondents are requested to be as brief c 

 -in all cases required as proof of ^ood /ait/t, 



Tvjenty copies of the number containing his 

 free to any correspondent on request. 



The editor will be glad to publish any queries consonant with the character of 

 the journal. 



Dew-Point and Predictions of Weather. 



One of the most serious drawbacks to a discussion and utiliza- 

 •tion of humidity records has been the lack of proper observational 

 methods, and also of tables of reduction. As late as 1884 we find 

 in Guyot two distinct tables for reducing observations with the 

 psychrometer (the usual instrument for determining humidity) 

 which give results differing by more than sixty degrees at extreme 

 ■dryness. Perhaps nothing can indicate better the hopelessness, as 

 late as 1887, of nearly all attempts at solving the problem of the 

 ■relation between the dry and wet thermometers and the dew-point, 

 than the announced determination of the meteorological committee 

 to omit a table for the psychrometer from their compendium of 

 tables for international use. It will be generally admitted that such 

 -a table is the most important and most needed of any in meteorol- 

 ogy. The most serious difficulty in nearly all investigations has 

 been a lack of ventilation of the psychrometer. 



In September, 1883, the sling psychrometer, which combines all 

 the admirable qualities of perfect ventilation and accuracy, great 

 ^peed of action, and extreme portability, was adopted in this 

 •country.' 



With this the true relation between the quantities mentioned 

 above was determined in 1884, and published in February, 1885 ; 

 and this has been used in the latest tables, leaving nothing now to 

 be desired except observations to check the formula at extreme 

 •dryness, such as does not occur east of the Rockies. 



I propose to discuss a few recent observations with the sling 

 psychrometer. It might be a question as to the best form in which 

 to study the moisture of the air. The relative humidity, the dif- 

 ference between the dew-point and air temperature, the dew-point 

 itself, the absolute humidity, and the vapor pressure, have all had 

 advocates. It may be remarked that the second of these, being a 

 deduction from two quantities which are often rapidly varying in 

 opposite directions, seems a little uncertain. The fourth and fifth 

 .are similar to the third. 



The following propositions regarding the dew-point are set 

 "forth: I. The diurnal change in air temperature does not affect 

 the dew-point ; 2. The temperature change from day to day does 

 not change the dew-point; 3. The air temperature is generally 

 very near the dew-point at sunrise, and farthest from it at 2 or 3 

 -P.M. ; 4. The air temperature in its fluctuations from day to day 

 ■follows the dew-point ; 5. Direction and velocity of the wind do 

 not in general affect the dew-point ; 6. The same may be said of 

 'fluctuations in air-pressure ; 7. The most marked rise in the dew- 

 point occurs on the approach of a storm having an abundance of 

 rain and during rain itself (the time of beginning and ending of 

 rain cannot be foretold from the dew-point); 8. The most marked 

 fall in the dew-point is caused by the advance of a high area, as 

 was to be expected ; 9, The most marked feature of the dew-point 

 is its constancy, though at times it has a range in several days far 

 greater than the air temperature, yet it quickly recovers from a fall 



* My attention has just been called to the use of a sling psychrometer by Espy in 

 Philadelphia in 1834. His results, which were not entirely satisfactory, were far ahead 

 ■of his time, and till quite recently exceeded in accuracy all others since. As is so often 

 -■the case, they seem to have attracted little or no attention. 



or rise to a normal position, depending on the season and other 

 general causes ; lo. The dew-point is the same in all parts of a 

 quite extended region. 



The fourth of these is one of the more important, and seems to 

 follow from the third. We have usually been taught that the air 

 temperature on a clear night will continue to fall till the dew-point 

 is reached, when there will be condensation of moisture, and libera- 

 tion of latent heat, which will prevent the further fall in tempera- 

 ture ; but it will be found, that, except after a long rain and in a 

 fog, the air temperature never reaches the dew-point. Very often 

 on clear nights the latter falls, and draws the former after it. If 

 this proposition can be established, there may be a chance to pre- 

 dict changes in air temperature from the dew-point, though they 

 are very close together. 



On many accounts the seventh proposition is the most interesting 

 of all. Does the atmosphere in this case gradually sink down ? 

 This usually would increase the dryness. The wind does not ap- 

 pear to carry the moisture, for this steady rise occurs in a calm. 

 Moreover, the direction of the wind, as coming from the earth's 

 surface, makes little or no difference. It is very evident that the 

 dew-point cannot be used in predicting rain. Under the eighth 

 proposition it should be noted that the fall in the dew-point ceases 

 in a few hours, and long before the pressure has reached a max- 

 imum. The figures from Vhich these propositions arise will 

 shortly be published elsewhere. It would be gratifying if others 

 are stimulated to make similar research. H. A. Hazen. 



Washington, Jan. 16. 



Horns of the Prong-Buck (Antilocapra). 



The other evening, while reading an article on the Artiodactyla, 

 by Professor Cope, in the American Nattiralist for December, 

 1888, I was much surprised at finding the following note: "Antilo- 

 capra is sometimes separated from the Bovidas as the type of a 

 family, because it is said to sometimes shed its horn-sheath. This 

 character, were it really normal, has no significance sufficient for 

 the establishment of a family division" (Italics mine). 



This doubt as to the shedding of the horn-sheath was so entirely 

 foreign to what I had been led to believe, both by observation and 

 reading, that I took the pains to look over what little literature I 

 possess touching the subject ; and, finding it so uniformly in favor 

 of the shedding theory, I write, asking if your readers can give any 

 additional facts in the case. 



Owen {Anatomy of Vertebrates, London, 1868, vol. iii. pp. 626, 

 627) gives a description of the shedding of the horns, and growth 

 of new ones, noticed by Mr. Bartlett in the Zoological Gardens of 

 London in 1865 ; also notes of Dr. Canfield at Monterey, Cal., 

 from 1855 to 1857, on a young male in captivity. Dr. Canfield is 

 also quoted : " In the months of December and January I have 

 never killed a buck with large horns ; and at that time of the year 

 all the bucks appear to be young ones, because their horns are so 

 small ; whereas in the spring and summer months almost all the 

 bucks appear to be old ones, for their horns are then large and no- 

 ticeable." Dr. Canfield also slates that " in the summer months 

 the line of demarcation between the horn and skin from which it 

 grows is very apparent and abrupt ; whereas in winter there is no 

 demarcation, the horn being very soft at its base, and passing in- 

 sensibly into cuticular tissues, and the horny substance being cov- 

 ered thinly with hair." 



Gill (Arrangement of the Families of Matmnals, Washington, 

 1872, p. 72) says of AntilocapridcE : "Horns deciduous, peculiar 

 to the rutting-season (in both sexes), developed as pseudocorneous 

 sheaths, with agglutinated hairs on osseous cores originating from 

 the frontal bones." Gray {Hand-List of the Edentate, Thick- 

 skijined, and Ruminant Mammals in the British Museum, Lon- 

 don, 1873, p. 135) evidently believes in this shedding, because he 

 places Antilocapra under a separate sub-order, Dicranocera, in- 

 stead of merely a separate family. Mivart {Lessons in Elementary 

 Anatomy, London, 1883, pp. 245, 246), on ecderonic appendages, 

 says, " and only in an anomalous iorm, the prong-buck (Antiloca- 

 pra), are these horny structures shed at intervals;" Huxley (^ 

 Manual of the Anatomy of Vertebrated Animals, New York, 

 1883, p. 327), " But in the remarkable prong-horned antelope of 

 North America {Antilocapra) the horny sheath is annually shed, 



