OCTOBfR 1 6, 1890] 



NA TURE 



595 



exception to this rule, and it was absolutely essential that 

 its rate of expansion should be thoroughly investigated, 

 in order that storage bottles should not be filled to a 

 dangerous extent. For temperatures up to 36° C. a closed 

 dilatometer of glass was employed, the long cylindrical 

 bulb of 60 c.c. capacity and part of the stem being filled 

 with liquid chlorine, and the remainder of the stem with 

 chlorine gas. The whole apparatus was immersed in a 

 long cylindrical bath. For the lowest temperature, of 

 — 80°, the bath was filled with solid carbon dioxide. For 

 the determination of the specific gravity at the boiling- 

 point of chlorine, a bath of boiling liquid chlorine itself 

 was employed, no less than three kilograms being required. 

 Between the boiling-point and o' the substance used in 

 the bath was liquid sulphur dioxide. For the determina- 

 tion at zero powdered ice was employed, and for the 

 higher temperatures a water-bath kept in motion by an 

 air current. It was not possible to proceed higher than 

 36° with this apparatus, on account of the danger of ex- 

 plosion. The higher determinations were made by means 

 of a hydrometer suspended in liquid chlorine enclosed in 

 a tube of hard glass which was immersed in a glass water- 

 bath heated to the required temperature. 



It will be seen from the following table that liquid 

 chlorine is indeed a very expansible substance. The co- 

 efficient of expansion at 80° is already o'oo346, nearly 

 equal to that of gaseous chlorine, and is rapidly increas- 

 ing, so that before the critical temperature of 146° is 

 attained, the coefficient of expansion will be considerably 

 higher than that of the gas. 



Following is a table showing the pressure, specific 

 gravity, and coefficient of expansion of liquid chlorine 

 for every 5^ of temperature from — 80° C., calculated 

 from the formulae derived from the experimental data 

 obtained. 



NO. TO94, ^'OL. 42] 



An interesting result, which is not noticed by Dr. 

 Knietsch in his paper, is obtained on calculating the 

 specific volume of chlorine from the determination of 

 specific gravity at the boiling-point, — 33"-6. On dividing 

 the atomic weight 35-5 by r5575, the specific gravity at 

 the boiling-point, the number 228 is obtained for the 

 atomic or specific volume of chlorine, a number prac- 

 tically identical with that derived by calculation from the 

 numerous determinations of the specific volume of com- 

 pounds containing chlorine. 



In this respect chlorine resembles bromine and the 

 compound radicles NO, and CN, which were shown by 

 Prof.Thorpe (Journ. Chem. Soc, 1880, 382) to occupy the 

 same volume in the free state as in combination. 



A. E. TUTTON. 



ELECTRICAL STORMS ON PIKE'S PEAK. 



'X'HE "Annals of the Astronomical Observatory of 

 ■■■ Harvard College," vol. xxii., contains the meteoro- 

 logical observations made at the summit of Pike's Peak, 

 Colorado, at a height of 14,134 feet above sea-level. 

 It is not remarkable that such an elevated station should 

 be celebrated for its electrical storms, and the observers 

 from 1874 to 1888 have recorded many interesting details 

 in the journals respecting their physical and physiological 

 actions. 



The manifestation of atmospheric electricity by induced 

 effects is often very strongly marked. During the passage 

 of electrified clouds over the summit of the peak the 

 well-known singing and buzzing noises described as an 

 adjunct of St. Elmo's fire were heard to proceed from 

 the telegraph wires, the exposed instruments, the instru- 

 ment shelter, and the house. The sound is said to be 

 very similar to the buzzing of bees and crackling of burning 

 evergreens. At times the hair of the observers became 

 upright and strongly repellent, and the same peculiar 

 noise proceeded from it. 



Some very remarkable effects are recorded on August 

 18, 1877: — "During the evening the most curiously 

 beautiful phenomena ever seen by the observer were 

 witnessed, in company with the assistant and four visitors. 

 Mention has been made in journal of May 25 and July 13 

 of a peculiar 'singing' or rather 'sizzing' noise on the 

 wire, but on these occasions it occurred in the day-time. 

 To-night it was heard again, but the line for an eighth of 

 a mile was distinctly outlined in brilliant light, which was 

 thrown out from the wire in beautiful scintillations. Near 

 us we could observe these little jets of flame very plainly. 

 They were invariably in the shape of a quadrant, and the 

 rays concentrated at the surface of the line in a small 

 mass about the size of a currant, which had a bluish 

 tinge. These little quadrants of light were constantly 

 jumping from one point to another of the line — now 

 pointing in one direction and again in another. There 

 was no heat to the light, and when the wire was touched 

 only the slightest tingling sensation was felt. Not only 

 was the wire outlined in this manner, but every exposed 

 metallic point and surface was similarly tipped or covered. 

 The anemometer cups appeared as four balls of fire 

 revolving slowly round a common centre : the wind-vane 

 was outlined with the same phosphorescent light, and 

 one of the visitors was very much alarmed by sparks 

 which were plainly visible in his hair, though none 

 appeared in the others'. At the time of the phenomenon 

 snow was falling, and it has been previously noticed that 

 the ' singing' noise is never heard except when the atmo- 

 sphere is very damp, and rain, hail, or snow is falling." 



These displays were described with the same minute- 

 ness on June 7, 1882. It was then noticed that when 

 the finger was passed along the line the little jets of flame 

 were successively puffed out, to be instantly relighted in 

 the rear. An observer also found that when he approached 



