754 



SCIENCE 



[N. S. Vol. XLIV. No. 1143 



ton district. He outlines clearly the synoptic 

 chart method, the basis of all American 

 weather forecasts. The general control of the 

 weather through atmospheric changes of pres- 

 sure are shown, with their general course from 

 west to east. Illustrating typical lows by 

 charts, he indicates seven separate types : cir- 

 cular, secondary, V-depressions, cols or sad- 

 dles, anti-cyclone, wedge-shaped and straight 

 isobars. The result of such typical forma- 

 tions are discussed quite fully. 



Speaking of the maps of temperature and 

 pressure changes, the two most valuable charts 

 in forecasting, an error is committed in speak- 

 ing of them as made thrice daily. The writer 

 reduced the observations from tri-daily to 

 semi-daily about thirty years since — a great 

 reduction in expense, much criticized at the 

 time, but which did not reduce the efficiency 

 of the service. 



While the associations of high temperatures 

 with low pressures, and of low temperatures 

 with high pressures are noted, yet Henry 

 frankly admits that allobars — the technical 

 term for areas of pressure changes — remain a 

 mystery. Forecasts from katallobars, areas 

 of falling pressure, are considered under the 

 headings : changes in form, greatest fall at 

 center in twelve hours, and concentration of 

 fall. While allobars are perfected in twelve 

 hours in Canada, the time increases south- 

 ward to thirty-six hours in the Gulf States. 

 The memoir on highs and lows is quite com- 

 plete. Henry points out that " the movement 

 of lows seems to coincide with the seasonal di- 

 rection of the planetary winds, of which they 

 are doubtless a part," and states that the 

 " speed of lows varies directly with the 

 strength of the general winds." As to precipi- 

 tation, in addition to other comments, he con- 

 siders that " when the high is north or north- 

 east of the low, the tendency to unsettled 

 weather and precipitation in the regions be- 

 tween them is at a maximum." The lows are 

 considered by groups, according to their pri- 

 mary appearance, as follows : North Pacific, 

 South Pacific, Alberta, Northern Rocky Moun- 

 tain, and Colorado, Texas, East Gulf, South 

 Atlantic. Highs are similarly treated. 



Forecasting in the Washington district, by 

 Henry, contains treatment of seasonal influ- 

 ences. He gives for Ohio five rules for warmer 

 weather, and six for colder weather. It would 

 have been most valuable if he had added sim- 

 ilar rules for other states. As to the prolonged 

 heated terms in the middle Western States 

 Henry says: 



They are probably due to fundamental causes in 

 the general circulation, the nature of which we do 

 not know. 



They end with the disintegration of a south- 

 eastern high and the formation of a north- 

 western high. 



Cold-wave forecasts are fully treated by 

 Professor H. J. Cox, who finds the pressure- 

 change charts far the most important element 

 therefor. Cold waves usually occur through 

 the rapid advance, with steep barometric gra- 

 dients, of highs in rear of well-marked lows. 

 Cox describes the various types of cold-waves, 

 and sets forth the effect thereon by topography, 

 especially by the Great Lakes and by the prox- 

 imity of the ocean. Well-selected charts illus- 

 trate the formation and advance of such waves. 

 He points out that atmospheric conditions for 

 vast distances, even over an area of 4,000 sq. 

 miles, are potent factors, through temperature, 

 pressure, humidity, pressure gradients, cloudi- 

 ness and snow-covered areas. 



Supplementary to cold waves Cox discusses 

 frost warnings, indicating the modifying influ- 

 ences of topography, especially in the shape of 

 large bodies of water, moist soils and drained 

 land. He also dwells on the different effects 

 of fast and of low moving highs, the latter 

 often producing frosts for successive nights. 

 Dew-point readings in the evening are consid- 

 ered fallacious indications as to frosts, while 

 humidity percentages have influences not 

 clearly understood as yet. 



Local peculiarities as to cold waves- and 

 frost-warnings, of much value and interest, are 

 presented by Forecasters John W. Smith, of 

 New England, L. M. Cline for the West Gulf, 

 F. H. Brandenburg for Denver, E. A. Bealls 

 for the North Pacific and G. H. Willson for 

 the South Pacific. These experienced fore- 



