THE DEVELOPMENT OF METEOROLOGY. 47 
carrying only self-recording instruments has been per- 
fected by Teisserenc de Bort, of Paris, and Assmann, of 
Berlin, until it largely replaces the manned balloon ; and as 
it can ascend to greater heights, it becomes our most powerful 
apparatus for exploring the upper atmosphere. At present 
the limiting height attained by kites is about 20,000 meters, 
and by sounding balloons, so called, 25,000 meters, although 
these limits are only attainable under the most favorable cir- 
cumstances. The persistent use of kites at Mr. Rotch’s ob- 
servatory at Blue Hill and the development of the mathe- 
matical theory of the kite by Professor Marvin stimulated all 
European observers to undertake the same line of research, 
each in his own country. Mr. Rotch has also been success- 
ful in securing the means 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 afterward at his new observa- 
tory 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 sta- 
tions extended from April to November, 1898. The average 
results as to vertical gradients of temperature, humidity, and 
wind were compiled by Dr. Frankenfield (see Weather Bu- 
reau Bulletin F), but the preparation and study of a daily 
map of the upper atmosphere analogous 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 embodied 
in a memoir prepared by his pupil, J. W. Sandstrom (pub- 
lished by the American Philosophical Society), elucidating 
