22 JOURNAL OF SCIENCE. 
difficulty of discriminating between genuine specific forms and 
fertile cross productions would be almost insurmountable by 
mere museum work, the results would be an unduly augmented 
descriptive enumeration of species. 
The question is a weighty one, as not only affecting safe sys- 
tematising, but also as bearing to some extent on the much 
discussed question of transmutation. Thus some additional 
light might be shed by local efforts of New Zealand naturalists 
on these important subjects. 
ESSAYS FROM THE BIOLOGICAL LABORATORY OF THE 
SCHOOL OF AGRICULTURE AT LINCOLN, UNDER 
THE SUPERINTENDENCE OF ROBERT VON LENDEN- 
FELD, Pu.D. 
—<>———. 
I.—On THE MOVEMENT OF CENTRES OF DEPRESSION OR HIGH PRESSURE 
THROUGH THE AIR.—By R. v. LENDENFELD, Ph.D. 
During my expedition to the central part of the New Zealand Alps a great 
many meteorological observatioas were made. On comparing the barometer 
readings with those of Lincoln and Hokitika, it appeared that the barometrical 
curves of these places could not be brought into harmony with those which I 
constructed for March, 1882, as observed on the Tasman Glacier, at an average 
height of 4000 feet. 
The barometrical curves of these three places were similar in shape, but not 
at such intervals one from the other as was to be expected. 
Hokitika lies about 30 west, and Lincoln about 125 miles to the east of the Tas- 
manGlacier. As the average rate at which these atmospheric centres travel is 300 
miles per 24 hours, the same pressure ought to be felt first on the Tasman Glacier, 
two hours and a-half later at Hokitika, and ten hours later at Lincoln, if, as is 
generally the case, the centre is travelling in an easterly direction. When drawing 
the three curves together, it appeared that the distance between the Lincoln and 
Hokitika curves averaged seven hours and a-half, as was to be expected, but that 
the curve for the Tasman Glacier was much further away from the other curves 
than the distance that would correspond to 30 and 125 miles, that is two and 
a-half hours and ten hours respectively. 
The actual distance of the similar curves from each other showed that there 
was an interval of eight and a-half hours and sixteen hours respectively. In other 
words this means, that any peculiarity of pressure travelling from west to east 
appears on the Tasman Glacier six hours too soon. The reason for this is simply 
that my observations on the Tasman Glacier were taken at a height of 4000 feet, 
whilst Hokitika lies at the level of the sea, and Lincoln only 81 feet above it. 
From the fact that barometrical changes appear sooner in great elevations 
than at the level of the sea, it follows that the line of corresponding pressure. 
that is that line ascending from any point of the surface of the earth in which all 
barometer readings at the same moment reduced to the sea level are the same (a 
line in the centre of high or low pressure, or a straight line in a cylindrical sur- 
face of corresponding pressure in every other case) is not vertical, but that it is 
very slanting, forming an angle open in the direction in which the centre of 
depression or high pressure is moving. This angle is small, and averages in New 
Zealand from 5 to 10 degrees. 
This slanting position of the lines of corresponding pressure is caused by the 
friction of the air on the surface of the earth. If, say, a centre of low pressure 
is formed over Australia, the lines of corresponding pressure will be vertical. This 
disturbance of the atmospheric equilibrium moves towards the east, and causes a 
whirlwind around it. This whirlwind together with the low pressure centre move 
quickly in the upper layers of the air, where there is no friction, and are of course 
retarded near the surface of the earth. In consequence of this, the line of cor- 
responding pressure slants forward, so that often the western part of a passing 
whirlwind, say a south-wester, is blowing on high, whilst we are still in the east- 
ern part of the same whirlwind, a nor’-wester on the surface of the earth, 
