198 Half-Hours with the Old Naturalists. [April, 
its direction. In a special memoir on this subject Herr 
Sprung has shown that an intensification of the wind whilst 
the gradients remain unchanged is, under ordinary circum- 
stances, conceivable only if the angle of deviation is simul- 
taneously augmented. In fa< 5 t the observations made at 
eighteen stations in the interior of the Eastern Continent 
show, in the forenoon, on the average, a decided deviation 
of the wind in accordance with Dove’s law of deflection, 
whilst in the afternoon deviations in the opposite direction 
slightly predominate. The predominance of deviations of 
the wind along with the course of the sun — which is deter- 
mined by the position of the north temperate zone with 
reference to the predominating tracks of barometric minima 
— is increased in the forenoon, but decreased in the after- 
noon, by a cause aCting periodically. This cause is the 
descent, into the lowest stratum of the atmosphere, of 
masses of the upper air which are moving more rapidly and 
at a greater angle to the gradient. On account of the 
increased angle of deflection the track of the clouds 
deviates, as is well known, to the right hand of the wind. 
Observations on cloud-movements reveal, in the upper strata 
of the atmosphere, a daily period in the direction of the 
wind opposite to that which obtains below, quite analogous 
to the inversion in the period of its velocity. 
III. HALF-HOURS WITH THE OLD 
NATURALISTS. 
[Under this title we propose giving, from time to time, sketches of the lives 
and researches of the earlier investigators of living Nature.] 
I. JOHN SWAMMERDAM. 
Jjpg)ET us cross not merely the German Ocean, but the 
last two centuries, and visit Holland in the olden 
time : Holland which for her size and population 
produced more savants of mark than any other country of 
modern Europe ; Holland which amidst her eager and 
bustling commercialism found time and appreciation for the 
