ration (see fig. 16). This innovation, which fixed the
form of the conventional registering instrument until the advent of the
radiosonde, seems to have stemmed from a source quite outside
meteorology--the technology of the steam gauge. Richard's thermometric
element was the curved metal tube of elliptical cross-section that
Bourdon had developed several decades earlier as a steam gauge. Pressure
within such a tube causes it to straighten, and thus to move a pointer
attached to one end. Bourdon had opened it to the steam source. Richard
filled it with alcohol, closed it, and found that the expansion of the
alcohol on heating caused a similar straightening. His barometric
element was a type of aneroid, which Hipp had already used but which
Richard may have also adopted from a type of steam gauge. For a
recording mechanism, Richard was able to use a simple direct lever
connection, as the forces involved in his instruments, being
concentrated, were not greatly hampered by friction.[33] By 1900 these
simple and inexpensive instruments had relegated to the scrap pile,
unfortunately literally, the elegant products of the mass attack of
observatory directors in the 1860's on the problem of the
self-registering thermometer and barometer.[34]

Conclusions

In view of the rarity of special studies on the history of
meteorological instruments, it is impossible to claim that this brief
review has neglected no important instruments, and conclusions as to the
lineage of the late 19th century instruments can only be tentatively
drawn. The conclusion is inescapable, however, that the majority of the
instruments upon which the self-registering systems of the late 19th
century were based had been proposed and, in most cases, actually
constructed in the 17th century. It is also evident that in the 17th
century at least one attempt was made at a system as comprehensive as
any accomplished in the 19th century.

[Illustration: Figure 16.--Richard's registering aneroid barometer, an
instrument used at the U.S. Weather Bureau about 1888. The Richard
registering thermometer is similar, the aneroid being replaced by an
alcohol-filled Bourdon tube. (_USNM 252981; Smithsonian photo
46740-C_.)]

To attribute the success of self-registering instruments in the late
19th century to the unquestionable improvements in the techniques of the
instrument-maker is to beg the question, for it is by no means clear
that the techniques of the 17th-c