82 REPORT—1845. 
by the rarefaction of the air over the land whilst the sun is in the northern 
signs, and its consequent overflow in the higher regions, producing a return 
current in the lower strata; and the increased pressure in the cold season. is 
occasioned by the cooling and condensation of the air, whilst the sun is on 
the south side of the equinoctial, and its consequent reception of the overflow 
in the upper strata from the regions which are then more powerfully warmed, 
and which is but partially counteracted by the opposite current in the lower 
strata. 
In concluding this communication, I beg respectfully to submit to the con- 
sideration of the eminent meteorologists here present, that it is very important 
towards the progress of this science, that the propriety (in such discussions 
as the present) of separating the effect of the two elastic forees which are 
considered to unite in forming the barometric pressure, should be speedily 
admitted or disproved. ‘The very remarkable fact recently brought to our 
notice by Sir James Ross, as one of the results of his memorable voyage, that 
the mean height of the barometer is full an inch less in the latitude of 75° S. 
than in the tropics, and that it diminishes progressively from the tropics to 
the high latitudes, presses the consideration of this point upon our notice; 
for it is either explained wholly or in greater part by the diminution of the 
vapour constituent in the higher latitudes, which diminution appears nearly 
to correspond throughout to the decrease of barometric pressure observed 
by Sir James Ross; or it is a fact unexplained, and I believe hitherto unat- 
tempted to be explained, on any other hypothesis, and of so startling a cha- 
racter as to call for immediate attention. 
If, by deducting the tension of the vapour from the barometric pressure, 
we do indeed obtain a true measure of the pressure of the gaseous portion 
of the atmosphere, the variations of the mean annual gaseous pressure, which 
will thus be obtained in different parts of the globe,—and the differences 
of pressure in different seasons at individual stations,—may be expected to 
throw a much clearer light than we have hitherto possessed on those great 
aérial currents, which owe their origin to variations of temperature proceed- 
ing partly from the different angles of inclination at which the sun’s rays 
are received, and partly from the nature and configuratioa of the material 
bodies at the surface of the earth: and a field of research appears to be thus 
opened by which our knowledge of both the persistent and the periodical 
disturbances of the equilibrium of the atmosphere may be greatly extended. 
Report on the Physiological Action of Medicines. By J. BLAKE, 
M.B., F.R.CS. &c. &c. 
Tue present report is but a continuation of that which was read at the last 
Meeting of the Association, and which has since been published in the Trans- 
actions. The investigation of the action of medicines has been confined to 
the observation of the effects that follow their direct introduction into the 
blood, by means of injections into the arteries or veins, and in most instances 
the hemadynamometer has been used, in order to ascertain more accurately 
the effects produced on the heart and vascular system. Although this view 
of the subject may appear to be of no practical utility, yet I trust that the 
results arrived at will justify the course that has been pursued. In my for- 
mer memoirs on this subject I have endeavoured to prove that isomorphous 
substances, when introduced directly into the blood, exert an analogous in- 
fluence on the animal economy. The experiments I am about to bring for» 
