28 REPORT—1862. 
a certain degree, of definite direction, and also of steering-power, and in obviating 
the objection to hydrogen balloons, which consisted in the expense of this gas, as a 
descent could be effected without loss of gas; hence smaller and much more ma-~ 
nageable balloons might be constructed than those now in use, and propulsion by 
means of a screw would be so much easier. 
Steering-power being obtained,Dr. Ashe hoped that a modification of shape might 
be found practicable, so as to present a minimum of resistance to propulsion by the 
screw. He proposed to steer by means of two small screws connected by a cranked 
axle placed at right angles to the action of the propeller, and situated in front of 
the car, so as not to interfere’with the hoisting of the propeller; these steering= 
screws should have their spirals turned in the same direction, and by revolving them 
in one direction, or the reverse, the balloon might be made to rotate on its vertical 
axis as might be desirable. The disagreeable rotation incident to balloons might 
also thus be obviated. Dr. Ashe suggested the employment of balloons in the in- 
vestigation of aérial currents and circular storms, and for the exploration of unknown 
continents: water, that great desideratum in such explorations, could be observed 
from an elevation when it would otherwise be passed by unobserved, and a descent 
being effected by the screw, its position might then be taken by observation, and 
marked for the guidance of foot explorers. Similar remarks would apply to the 
discovery of the easiest routes by means of balloon observations, 
On some Improvements in the Barometer, By Isaac Asue, MB. 
The author suggested a contrivance by which a water-barometer might be con- 
structed, having a tube of not more than 3} feet in length, with a range in the 
height of the column of liquid equal to about 39 inches. Though correct in theory, 
this contrivance seemed to have some defects which would practically interfere with 
its accuracy. 
On the Determination of Heights by means of the Barometer, By Joun Bax. 
The object of this paper was to direct attention to the serious errors which are in- 
volved in the ordinary process of reducing barometric observations taken for hypso- 
metrical purposes. This process involves two assumptions: Ist, that the volume 
of a column of air unequally heated is nearly the same as that of an equal weight 
of air of the same mean temperature ; 2ndly, that the mean temperature of the 
column or stratum of air between the stations of observation corresponds to the 
mean of the readings of thermometers standing in the shade at each station. The 
error involved in the first assumption is not very considerable ; that arising from 
the second is, on the contrary, highly important. 
M. Brayais, who along with M. Charles Martins has contributed largely to our 
knowledge of the meteorology of the Alps, was the first to propose a practical plan 
for applying a correction to the assumed mean temperature of the air depending 
upon the hour of the day and the season of the year at which observations are 
made, but it is to M. Plantamour, the distinguished astronomer of Geneva, that we 
owe the fullest investigation of this important subject. 
Having ascertained by careful levelling the true height of the Great St. Bernard 
above Geneva, M. Plantamour finds that the mean of all the barometric observa- 
tions, made during eighteen years, deviates by fourteen English feet from the true 
height, and he attributes this deviation, with great apparent probability, to an ab- 
normal depression of the mean temperature of Geneva, owing to the neighbourhood 
of the lake. 
The readings of the barometer and thermometer at the observatories of Geneva 
and the St. Bernard are taken daily at nine hours or epochs. M. Plantamour 
assumes that, on an average of a long period of years, the mean of the observations 
taken at any one epoch in the twenty-four hours should give the true difference of 
height between the two stations, with an error due to the difference between the 
mean of the readings of the thermometers at both stations at the same epoch, 
and the true mean temperature of the air in the intervening stratum. Calcula- 
ting then the height of the St. Bernard by the elements corresponding to each 
epoch of the day during the four summer months, from June to September, 
