142 
THE COURSE OF STORMS. 
of the storms of the temperate latitudes partake of the same 
nature essentially as the tropical hurricanes. 
Since the date of Eeid’s work, and especially within the last 
twenty years, a great impulse has been given to the study of 
this branch of meteorology. Several causes have contributed to 
this — the establishment of Meteorological Societies in various 
countries, the multiplication of observers (without whose aid 
nothing can be done), and, perhaps most of all, the introduction 
and application of the electric telegraph. The advantage of the 
telegraph to meteorology has been mainly indirect. For purposes 
of study the storms of last year are as valuable as those of 
yesterday, and more so, inasmuch as they admit of the observa- 
tions being more complete. But what the telegraph has done for 
meteorology is this. It has created a kind of living interest in the 
study, and, by holding out the prospect of immediate practical appli- 
cation, it has stimulated the Governments of various countries 
to organise systems of observation to an extent, which could 
hardly have been compassed, either by individuals or by societies. 
The great meteorological achievement of the last twenty years 
has undoubtedly been the establishment of the principle, that all 
great atmospheric commotions, in whatever part of the world 
they occur, are essentially cyclonic in character — that is, that 
they partake of the same nature as the so-called cyclones, or 
circular storms of the tropics. We may even go further than this, 
and apply the same law to those minor atmospheric movements, 
which are concerned in the ordinary weather changes with which 
we are familiar. This becomes obvious enough when we examine 
an isobaric chart of any considerable tract of the earth’s surface. 
An isobaric chart is a chart, upon which the lines of equal 
barometric pressure are marked — the isobaric lines, as they are 
called, or sometimes, for shortness’ sake, isobars. One of the 
most valuable series of charts of this kind that have yet been 
published, is that constructed by Captain Hoffmeyer, of Copen- 
