PROCEEDINGS. 
513 
At the height of 12,000 feet the neck of the balloon opened and large 
quantities of gas flowed out, so that the sudden rise was immediately 
followed by a more sudden fall, and to check the impetus and avoid 
striking the ground, much more ballast was thrown out. This carried the 
balloon up over 1,000 feet, and as the ballast was now exhausted a land¬ 
ing was made at Hoffman, Illinois, 54 miles from St. Louis. 
The second voyage was made in the “ Great Northwest,” on August 13 
1887, from Philadelphia, to a height of 7,070 feet.. Both of these voyages 
showed a remarkable adaptability of the sling psychrometer for balloons* 
In the most rapid ascent or descent the temperature was obtained within 
about 1° F., while in other voyages errors of 15° have been noted, owing 
to the sluggishness of the still thermometer. The scientific results were 
of the highest interest, and show what may be hoped for meteorology 
in the future of ballooning. The preceding table exhibits the more im¬ 
portant determinations. 
Mr. Thomas Russell made a communication on Baudin’s 
Vertical Minimum Thermometer a Marteau. 
318th Meeting. April 14, 1888. 
The President, Mr. Mallery, in the chair. 
Forty-eight members and guests present. 
Mr. C. O. Boutelle read a paper on Geodetic Azimuths. 
[Abstract.] 
1. Account of difficulties found in use of glass roofs for protection of 
mercurial horizons, owing to unequal surfaces, densities, and other imper¬ 
fections shown by the best French plate glass while observing for azimuth 
at Seaton station, in Washington, in December, 1868. 
2. They were overcome in 1870 by the substitution of thin semi-trans¬ 
parent gauze for glass in all the more delicate class of observations where 
a reflecting surface of mercury is used. 
3. Geodetic observers have, as a rule, settled upon observations of close 
circumpolar stars as the best method of obtaining good' azimuths. The 
simplest method is that of observations of Polaris in any part of its orbit. 
Polaris is chosen because its place is best determined and because its size 
and brilliancy make it peculiarly available for accurate pointing with field 
telescopes. 
4. A comparison was made between the results of observations made 
upon Polaris for azimuth, in Spain, in 1879, where a striding-level was 
66—Bull. Phil. Soc., Wash., Vol. 11. 
