40 



SCIENTIFIC NEWS. 



[Jan. 13, 1 8 



prognostics as a distinct and important branch, and one 

 on wliich the sailor, the fisherman, the shepherd, and 

 the " solitary observer," for whom one chapter is specially 

 written, must relj^, if he does not see the daily chart in 

 the Times or elsewhere. 



The first step which most persons take in the science 

 of meteorology, is to expect fine weather when the 

 barometer rises, and bad weather when it falls. The 

 second step is to be so discouraged by the number of 

 exceptions to this simple rule as to place little or no 

 value on this instrument, which is imagined by some 

 people to indicate rain as clearly as a thermometer shows 

 temperature. The third step should be to read Mr. 

 Abercromby's book. "Weather" in its strict sense is 

 used to denote the actual appearance of the sky, the 

 presence or absence of clouds, and whether rain, snow, 

 or hail are falling, and excludes temperature and wind. 

 It is generally known that there are two systems of 

 recording the weather. The older method consists of a 

 continuous chart, on which the fluctuations of the 

 barometer, thermometer, direction and force of wind, and 

 amount of rainfall are indicated bj' lines, which refer to 

 appropriate scales of the various quantities. These 

 charts generally show the successive changes that have 

 taken place during one week at a certain observing 

 station. The more modern system, which by no means 

 supersedes the other, but forms a very important sup- 

 plement to it, has been introduced within the last twenty 

 years, and exhibits the state of the weather at a certain 

 instant for a large number of stations. 



By this method, a chart of a large area of the earth's 

 surface is taken, and after marking on the map the 

 height of the barometer at each place, lines are drawn 

 through all stations at which the barometer marks a 

 particular height. Thus a line would be drawn through 

 all places where the pressure was 30-0 inches, another 

 through all places where it was 29 '8 inches, and so on at 

 any intervals which were considered necessary. These 

 lines are called "isobars," because they mark out lines 



of equal pressure After the isobars have been put 



in, lines are usually drawn through all places where the 

 temperature is equal at the moment. Then arrows to 

 mark the velocity and direction of the wind are inserted, 

 and finallj' letters, or other symbols, to denote the ap- 

 pearance of the sky, the amount of cloud, or the occur- 

 rence of rain or snow. Such a chart is called a " synoptic 

 chart." These are familiar to all readers of the Times, 

 and constitute not only the source of our knowledge of 

 many important facts in the science of weather which it 

 was impossible to deduce from statistics, and explain why 

 certain observations are quite useless, but enable very 

 trustworthy forecasts to be made. This system of fore- 

 casting will undoubtedly be to most readers by far the 

 most interesting part of the book. It is surprising that 

 so little is known of the teachings of synoptic charts, for 

 they are not in their infancy. It is impossible to give 

 an idea in a short notice such as the present of the rela- 

 tions of wind and weather to isobars, but the following 

 extract summarises the important generalisations which 

 have been discovered, and will give an idea of some of 

 the most interesting topics of the book. 



1. That in geneial the configuration of the isobars 

 assumed one of seven well-defined forms. 



2. That, independent of the shape of the isobars, the 

 wind always took a definite direction relative to the trend 

 of those lines and the position of the neaiest area of low 

 pressure. 



3. That the velocity of the wind was always nearly 

 proportional to the closeness of the isobars. 



4. That the weather — that is to say, the kind of cloud, 

 rain, fog, etc. — at any moment was related to the shape, 

 and not to the closeness of the isobars, some shapes 

 enclosing areas of fine, others of bad weather. 



5. That the regions thus mapped out by isobars were 

 constantly shifting their position, so that changes of 

 weather were caused by the drifting past of these areas 

 of good or bad weather, just as on a small scale rain 

 falls as a squall drives by. The motion of these areas 

 was found to follow certain laws, so that forecasting the 

 weather changes in advance became possible. 



6. That sometimes in the temperate zone, and 

 habitually in the tropics, rain fell without any appreciable 

 change in the isobars, though the wind conformed to the 

 general law of these lines. 



The book is well illustrated by a number of typical 

 and actual charts and diagrams, and a few less satisfac- 

 tory representations of clouds. It is a great convenience 

 to the reader if a diagram, to which constant reference is 

 made, is placed on the left-hand page. Fig. i would be 

 much more easily referred to if it were printed on page 

 24 or 26 instead of in its present position. Where the 

 whole of the reference to the figure is contained on one 

 page, as at Fig. 54, this is of no consequence. We 

 notice a misprint, marked for masked, on p. 158, and air 

 instead of wind on p. 35. The author falls into a some- 

 what amusing mistake on p. 115 : " On one occasion the 

 interval between the lightning and the thunder was five 

 seconds, while the rain did not arrive for nineteen 

 seconds. Now, calculating the distance of the origin of 

 the lightning from the velocity of sound, we find the 

 altitude to be 5,500 feet ; while the distance through 

 which a drop would fall in nineteen seconds would have 

 been 5,800 feet. The difference is only 300 feet, which 

 is very little, considering the nature of the observations 

 and the unknown retardation of a falling drop from the 

 resistance of the air." Taking a drop as ^pLj- of an 

 ounce, the effect of the blow, if it were to fall 5,800 feet 

 in nineteen seconds, would be equal to that of one ounce 

 falling 25 feet, or a quarter of a pound falling about 

 19 inches. We pause for a moment to let a four-ounce 

 weight from a letter-balance fall from this height on our 

 knuckles, and cannot help realising that we owe a debt 

 of gratitude to the resistance of the air. It is probable 

 that after the first 5 or 10 feet, a drop falls at the uniform 

 rate of 18 to 20 feet a second. This allows less than 

 400 for the case described by the author, whom we must 

 leave to account for the discrepancy. 



Experimental Chemistry for Junior Students. Part IV 

 By Professor Emerson Reynolds, M.D., F.R.S., F.C.S- 

 London : Longman, Green, and Co. 



This work concludes the author's course of Experi- 

 mental Chemistry, and is the most readable organic 

 chemistry with which we are acquainted. Commencing 

 with the manufacture of methyl and ethyl alcohol, the 

 author builds up synthetically most of the compounds he 

 describes. The student who carefully performs the 

 experiments mentioned in this book will find he has 

 obtained a very fair insight into this branch of chemistry. 



We regret the author has not provided this useful 

 little book with an index, but this omission will probably 

 be remedied in the next edition. 



In the appendix a description is given of Victor 

 Meyer's method of determining vapour densities. 



