430 
NATURE 
[Sep¢, 28, 1871 

METEOROLOGY IN AMERICA * 
III].—SELF-REGISTERING INSTRUMENTS 
fare e as is the ordinary barometer, the most 
valuable instruments are those which are automatic, 
or self-registering. Prominent among those used in 
America are the Self-recording Barometer and Meteoro- 
graph invented by Prof. G. W. Hough, Superintendent 
of the Dudley Observatory. Lord Rosse’s telescope has 
not done more for astronomy than will the self-regis- 
tering barometer do for meteorology. 
The diagram, Fig. 7, will illustrate the method of regis- 
tering the height of the barometer and thermometer on a 
single sheet, by the use of one set of mechanism in these 
simple yet complete and consummate contrivances. 
Let D be a drum six inches in diameter and seven 





inches in height, covered with a sheet of ruled paper. 
This drum is presumed to revolve at any convenient rate, 
say one inch per day, Let L be an iron or brass bar 
twenty-four inches in length, mounted on an axis passing 
through the point c. Let P be a steel pen attached to the 
end of the lever projecting over the centre of the drum. 
Let P’ and P” be platinum wires attached to the lever at 
three inches on either side of the axis ¢c. The wire P’ is 
over the shorter leg of a siphon barometer, and the wire 
P” passes into the end of an open mercury thermometer. 
Nowif the lever L be elevated at the end over the drum, 
the wire P’ will touch the top of a float resting in the 
shorter leg of the siphon barometer If then a battery, 
B, and electro-magnet, E, be arranged as in the diagram, 
when contact is made with the float, a current of electri- 
city will pass through the circuit, and the electro-magnet 
E is operated. 

If then, when the circuit is completed, a 


BAROMETER 
MOMETER 
ER 
im 
Hy LAH 
TH 
FIG. 7-—REGISTRATION OF THE HEIGHT OF BAROMETER AND THERMOMETER 
blow be struck on the pen P, by means of the electro- 
magnet, or a hammer unlocked by it, the dot on the drum 
sheet will indicate the height of the barometer at that 
time. Itis obvious that as often as the lever is elevated a 
record will be made. For the barometer an hourly record 
will be found to be sufficient. 
If the lever L is rigid and firmly mounted, the mere 
measurement of height by means of electrical contact can 
be carried to almost any degree of precision. 
It was found from numerous experiments made some 
years since, that the magnetic circuit is not completed for 
a distance of one ten-thousandth of an inch. Therefore, 
whatever source of error there may be in the results re- 
corded by this method is due to the barometer itself. In 
* We are again indebted to Harper's New Monthly Magazine for the 
continuation of the article by Prof. Maury, and the woodcuts which we re- 
produce this week. 
practice, from records extending over nearly one year, it 
is found that the results are inside the errors of reading 
from the drum sheet. 
A long experience has led to the conclusion that this 
degree of precision is sufficient for the investigation of 
barometric changes, and is but little outside the limit of 
error from reading a standard barometer. 
An examination of the diagram will also show at a 
glance how the height of the thermometer is recorded. It 
should, however, previously be stated that the thermo- 
meter is a little larger than those in ordinary use, and has 
a platinum wire, a, cemented in the bulb, communicating 
with the mercury in the inside. 
The following is a general description of a machine 
constructed for the Signal Service at the request of the 
chief signal officer. 
It registers hourly the barometer and wet and dry bulb 

