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Vol. XV. NEW YORK, June 27, 1890. No. 386. 



CONTENTS: 



The Cherokees in Pre-Colum- Vertical Components of Motion 



BiAN Times. Cyrus Tftomas... 379 ' i^i Cyclones and Anticyclones. 



Notes and News 384 i 



The Tornado : Espy's Experi- 



ments. H. A. Hazen . 



Letters to the Editor. 

 Ohio Meteorites. 



Warren K. Moot'ehead '. 



W. M. Davis I 

 Book-Reviews. 



Locke 



Kussig: its People and its Liter- 

 ature 



Pestalozzi, his Life and Work 



Among the Publishers 



THE TORNADO: ESPY'S EXPERIMENTS. 



These investig-ations of Espy upon what aetions may be 

 considered as taking place in the upper air, as has been al- 

 ready said, are of the highest importance, and demand a 

 special consideration. A proper interpretation of his re- 

 sults will help us in all our studies and reasonings. One of 

 the most serious difficulties that we shall encounter, how- 

 ever, is in the fact that in the open air we are not dealing 

 with a limited confined space, but we have to do with un- 

 limited space and a well-nigh frictionless medium. 'The 

 apparatus which he used has been sufficiently described 

 already. The earlier investigation with the nephele- 

 scope was made witliout the use of a condensing syringe; 

 and in this we are able to compreherid clearly just the 

 action which took place, while in the later researches the 

 results were quite complex. Mr, Espy first carried his jar 

 into air the temperature of which was quite low, at freezing 

 or below; and, after it had attained the temperature of 

 its surroundings, the stop-cock was closed, and the jar was 

 taken to a room with high temperature, 70° to 80°. The air 

 inside was expanded by the heat, and the amount of this 

 expansion was measured on the gauge. He then opened the 



stop cock, and closed it at the moment the mercury reached 

 a level in the gaug'S. The rising of the mercury in the 

 gauge after explosion, he thought was due to the gradual 

 heating of the air which had been cooled by the sudden ex- 

 pansion. In the same way the jar was left in a high tem- 

 perature for a time; then the stop-cock was closed, and it 

 was carried to a low temperature. In this case, of course, 

 the mercury in the gauge had the opposite motion to that it 

 had before. The same experiments were tried with both 

 moist and dry air. 



One of the more important results from these researches, 

 Espy does not seem to have thought of, though it dimly 

 foreshadowed the epocli making experiments of Mayer and 

 Joule, in England, on the mechanical equivalent of heat. 

 It is plain that in this confined space used by Espy there 

 must be a relation between the amount of rise or fall in 

 temperature and the corresponding change in air-pressure 

 under a constant volume, and this will enable us to deter- 

 mine the expansion of air per degree of heat applied. In 

 moist air the average difference of temperature between the 

 cold and warm room was 45*^, and the rise of the gauge 2.97 

 inches; in moist air, going from a warm to a cold room, the 

 fall in temperature was 45°, and the fall in the gauge 2.60 

 inches: while with dry air these quantities were 57° and 

 3.34 inches and 63° and 3.30 inches respectively. The 

 amount of change per degree in the four cases was .066, 

 .057, .059, and .052 of an inch, or a mean of .059 of an inch 

 in all the cases. The reading of the barometer is not given ; 

 but, if we assume it to be 29.80 inches, we fl.nd that the in- 

 crease of temperature required to double the pressure in the 

 jar was not far from 505°, — a result which is remarkably 

 close to the 490° found by the more careful and extended re- 

 searches of others. We now see the important bearing of 

 this first work on our studies. If we compress air 5 inches 

 by the gauge, we would heat it 83°; and if 10 inches, 167°; 

 and so on, provided no heat was lost or dissipated in the 

 operation. We ought also to be able to calculate from the 

 reading of the gauge, after any operation of either conden- 

 sation or expansion, exactly how much the air was heated 

 or cooled, provided always that no heat was lost or gained. 



In the light of this interpretation, let us examine some of 

 Espy's experiments. In one instance he compressed the air 

 10 inches. We may suppose that he waited long enough to 

 allow the jar to attain the air temperature before explosion. 

 After the explosion the gauge reading was 2.15 inches, which 

 would indicate that the cooling was not far from 36°, pro- 

 vided the only influence on the gauge was through the rise 

 of pressure consequent upon the heating of the air by sur- 

 roundings. It would appear that the theoretical cooling 

 from such an expansion should be much greater than this; 

 and, in fact, we cannot reason or theorize upor this result 

 in any way, without first learning tlie probable loss of heat 

 during compression, and its gain during expansion, to and 

 from the environment. Espy's nephelescope was duplicated 

 in its different parts, with the addition of a most delicate 

 thermometer loaned by Professor Russell. This instrument 

 has a bulb .06 of an inch in diameter and 1 inch in length, 

 and would change one degree in from two to three seconds. 

 It is plain, tiiat, in observations with any degree of speed 

 in change of temperature, any instrument will be liable to 

 -lag behind the existing temperature. This difficulty, how- 



