150 
WAT ORE 
[DECEMBER 17, 1896 
LETTERS TO THE EDITOR. 
(The Editor does not hold himself responsible for opinions ex- 
pressed by his correspondents. Neither can he undertake 
to return, or to correspond with the writers of, rejected 
manuscripts intended for this or any other part of NATURE. 
No notice is taken of anonymous communications, | 
The Use of Kites for Meteorological Observations in 
the Upper Air. 
ATTEMPTS to use kites for meteorological observations in the 
upper air began more than a century ago. The lack of light 
instruments which record automatically and continuously, pre- 
vented the success of the early experimenters. Such records 
are now obtained for the first time by means of kites at the 
Blue Hill Meteorological Observatory, near Boston. A history 
of kite-flying for meteorological observations, with a general 
account of the work at the Blue Hill Observatory, was given 
by the Director, Mr. Rotch, in a paper read before the Physical 
Section of the British Association at the Liverpool meeting 
(1896). Notes in NATURE of October 22 and 29, vol. liv. pp. 
595 and 629, mention briefly the altitudes to which a meteoro- 
graph has been lifted at Blue Hill during the past summer. A 
few of the details of the recent highest ascent may be of interest 
to the readers of NATURE, especially as it shows that clear and 
definite meteorological records can be obtained at a great height 
by means of kites, at a comparatively small expense. The 
meteorograph weighs three pounds, and records temperature, 
humidity, and atmospheric pressure. The record of October 8, 
from the earth’s surface to an altitude of 9375 feet above sea 
level, was as clear and sharp as the records of similar instruments 
in thermometer screens at the observatory. The temperature- 
scale on the chart is centigrade, and the humidity pen records 
10 per cent. too low, so that 90 per cent. represents saturation. 
The barograph-pen is made to record altitudes in metre; but 
it went entirely off the scale, which is’ too small for the altitude 
reached. The record was, however, completed on the part of 
the chart above the scale. A determination of the altitude was 
made by placing the barograph under an air-pump, and finding 
the fall of pressure necessary to raise the barograph-pen to the 
highest point recorded when on the kite. From the amount of 
fall and the temperature recorded by the thermographs on the 
kite and at the observatory, the altitude was computed. The 
altitude was also computed from the angular elevation of the 
kites and the length of line recorded by a reel, 3 per cent. 
being allowed for the sag of the steel wire holding the kites. 
The amount of the sag was determined by previous theodolite 
measurement, from a long base line, of the altitude of the 
kites. The altitudes by the two methods agreed within 1 per 
cent. of the height, and the mean of the two is given. In 
this ascent nine kites with a total area of about 170 square 
feet and 18,000 feet of steel wire, weighing about 46 lbs., were 
used, All the work of the ascent was managed with an 
ordinary wooden windlass by the three members of the staff— 
Mr. Fergusson, Mr. Sweetland and myself. The sea-coast is 
about six miles from Blue Hill, and the general level of the 
surrounding land is about 100 feet above sea-level. The top of 
Blue Hill, from which the kites were flown, is 635 feet above 
sea-level. Cumulus clouds had begun to form when the ascent 
began, and the meteorograph was soon elevated to the cloud- 
level, as shown by the humidity record, and was then lowered 
to remove a defective kite. In the second ascent the clouds 
were entered at an altitude of 4500 feet. The successive kites 
added to lift the line as they rose to the cloud-level, and again, 
when they were drawn below it, gave the data for numerous 
successive determinations of the altitude of the bases of the 
cumulus clouds, and furnish an example of the accuracy and 
frequency with which clouds can be measured in this manner, 
as shown by the following results :— 
am. p.m. 
Time ... 11.18 1.58 2.05 2.39 3-0% 3:34 3.36 4:34 4-57 5:23 
Altitude 2974 ft. 4500 4641 5035 5405 5254 5097 5044 5000 5130 
These measurements show that the level of the bases of the 
cumulus clouds rose steadily from 11 a.m. to 3 p.m., then 
diminished slowly. Theodolite measurements at Blue Hill show 
this to be the normal daily course of the cumulus. The kite- 
meteorograph passed above the tops of the cumulus at 3.08 p.m. 
and the humidity fell in a short time 46 per cent., showing a 
very dry air above the clouds ; a condition which the meteoro- 
NO. 1416, VOL. 55] 
graph has shown in every case when it was lifted above the 
clouds, the fall of humidity usually being very rapid after the top 
of the cloud is passed. 
The temperature on October 8 fell below the freezing point 
at 1.35 p-m. at an altitude of 4540 feet, and continued below 
freezing until an altitude of 3850 feet was reached at 8.24 
p-m. in the descent. At the highest point the recorded tem- 
perature was 10° below the freezing point. At the Blue Hill 
Valley Station at this time the temperature shown by a ther- 
mograph was 49° F., making a fall of 29° F. in 9300 feet, or 
I” in 320 feet. This fall is slower than the average we have 
found, which is about 4° in 1o0o feet during the day-time, 
or I” in 250 feet. During, and immediately preceding, de- 
cidedly colder weather the rate of fall increases to about 6° in 
1000 feet. The rate of fall is least preceding warmer weather, 
since a warm wave, as a rule, sets in first aloft. 
The ease with which a meteorograph can be lifted to the height 
of a mile is shown by the fact that this was accomplished three 
times in four days during August in normal weather conditions 
The highest point reached by no means represents the highest 
point attainable with kites, since at the time of the highest ascent 
the pull of the kites on the line was too lbs., while the breaking 
strain of the line is over 300 1bs., so that had there been more wire 
on the reel a much greater altitude might have been reached. 
Three, or possibly four or five, miles does not seem unattainable 
in this manner. The importance of such observations for the 
further developement of meteorology is shown by the fact that 
the weather conditions at the height of a mile above any 
station differ more from the weather at that station than does 
the weather at any place within 500 or 1000 miles at the level 
of the station on the earth’s surface. At the height of a mile 
in the free air the temperature is usually from 15° to 25° F. 
colder than at the earth’s surface, and there is virtually no daily 
change in temperature, the nights being as warm as the days. The 
only changes are due to the passage of warm and cold waves. 
During fair weather at this height the days are very damp, and 
the nights extremely dry. Low clouds frequently cover the 
earth, and even rain may fall from these while the sun shines 
bright at the height of a mile. The average velocity of the 
wind at this height is four times greater than at the ground, and 
hurricanes of 100 miles an hour are not uncommon. At least, 
the meteorograph records obtained by kites, and measurements 
of the heights and movements of clouds with theodolites, indicate 
that these are the conditions which exist above Blue Hill. 
H. Hetm CLayton. 
Blue Hill Meteorological Observatory, Milton, Mass., 
U.S.A., November 20. 
The Theory of Dissociation into Ions. 
ProF. ARMSTRONG (page 78) says that the chief concern 
of chemists has been to establish facts ; and perhaps this is true > 
but to an outsider it has seemed recently as if some few facts 
were unwelcome to the school of chemists represented by him- 
self. For instance, they seemed annoyed at one time with the. 
inertness and the specific-heat-ratio of argon; now he ex- 
presses himself as if vexed with the slowness of ionic velocities, 
and ‘‘ declines to accept it.” 
If the ions travelled quicker, a liquid would conduct better than 
it does, and perhaps that is what Prof. Armstrong desires ; but it 
is difficult to see any ground for his objection to the present 
state of things. Ina rare medium, like a gas, the ions migrate 
quickly ; in a dense medium, like a liquid, they migrate slowly ; 
and their numerical speeds, as measured, exactly for liquids, 
approximately for air, are not inappropriate to the relative 
crowdedness. What more can bedesired? The facts do not even 
demand much difference between the gaseous and liquid states ; 
though even if they did they would still have to be accepted, just 
as the facts of viscosity and its contrary affection by temperature 
in the two states have been accepted. 
I know very well, and have long known, that Prof. Armstrong 
objects to the idea of perfectly free ions ; but surely he is aware 
that many physicists object to it too, with whatever glimmering 
of chemical instinct they possess, and they have endeavoured to 
show that the facts can be expressed without such an hypothesis. 
Physicists have also objected to the idea of a dissolved salt 
existing as a free gas in a solvent, notwithstanding the remark- 
able analogies with gaseous laws, discovered in an admirable 
manner by physical chemists, that such a substance presents ; 
