302 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1907. 
with both balloons and kites since 1893 has constituted a brillant 
epoch in our study of the atmosphere. Although the kite had fre- 
quently been used by Franklin and other electricians during the 
previous forty years, yet its use to carry thermometers to great 
heights dates only from Alexander Wilson, of Glasgow, 1780. A 
century later it was employed in England to study the upper winds by 
E. D. Archibald. The invention of the Hargrave or box kite and the 
improvements introduced in every detail by Professor Marvin, and 
to a less extent by others, have converted the kite into a most impor- 
tant meteorological apparatus. Meanwhile the use of a small balloon 
carrying only self-recording instruments has been perfected by Teis- 
serene de Bort, of Paris, and Assmann, of Berlin, until it largely re- 
places the manned balloon; and as it can ascend to greater heights, it 
becomes our most powerful apparatus for exploring the upper atmos- 
phere. At present the limiting height attained by kites is about 
20,000 feet and by sounding balloons, so called, 25,000 meters, al- 
though these limits are only attainable under the most favorable cir- 
cumstances. The persistent use of kites at Mr. Rotch’s observatory 
at Blue Hill and the development of the mathematical theory of the 
kite by Professor Marvin stimulated all European observers to under- 
take the same line of research, each in his own country. Mr. Rotch 
has also been successful in securing the cooperation of Teisserenc de 
Bort for special kite explorations over the ocean. With characteristic 
energy, Assmann has been able to send up either a kite or balloon, or 
both, every day—first at Berlin, 1899-1902, and afterwards at his new 
observatory at Lindenberg; so that we have a continuous history of 
the temperature of the air above Berlin for several years, up to the 
highest points attained by kites and balloons. 
On the other hand, in the United States, the Chief of the Weather 
Bureau, after authorizing Professor Marvin to develop the kite, the 
reel, and the meteorograph, established seventeen kite stations north 
of a line joining Washington and Topeka, as a southern limit, with 
the intention of receiving the reports by telegraph and compiling a 
daily map of the conditions in the upper atmosphere. The work at 
these stations extended from April to November, 1898. The average 
results as to vertical gradients of temperature, humidity, and wind 
were compiled by Doctor Frankenfield (see Weather Bureau Bulletin 
F), but the preparation and study of a daily map of the upper atmos- 
phere analgous to the maps that we are accustomed to use at the sea 
level required a new line of thought for which the world was not quite 
prepared at that time. To this problem Prof. C. A. Bjerknes, of 
Stockholm, has paid especial attention, and his ideas have been em- 
bodied in a memoir prepared by his pupil, J. W. Sandstrom (pub- 
lished by the American Philosophical Society in 1904), elucidating 
the first steps proper to be taken in the reduction of the observations 
