1888.] occurred at Dacca on April 7th, 1888. 189 



District in 1875, as to size, duration, and general direction, but, as its 

 track lay through a populous town instead of the open country, the 

 amount of damage done by it was very large. 



Meteorological conditions usually preceding tornadoes. — As will 

 be seen from the preceding description, the number of tornadoes which 

 have occurred in Bengal (and probably in India also), and of which ac- 

 curate records are obtainable, has been far too small to enable any scientific 

 work to be undertaken as to their causation. In the United States, how- 

 ever, as previously mentioned, tornadoes are frequent, and, under the 

 direction of the War Department, the Signal Service of that country has 

 done most valuable work on these storms. For a full description of the 

 effects of these storms and of the meteorological conditions which pre- 

 cede them, the works of Lieutenant John P. Finley may be consulted.* 

 But even though Mr. Finley has worked out the records of about 800 

 tornadoes, he has been unable to lay down more than very general state- 

 ments as to the meteorological conditions which precede such storms, 

 and, in his last work published in 1885, he states, " The following are 

 some of the conclusions which appear to proceed from a study of the 

 relation of tornado-centres to areas of barometric minimum. 



1. That there is a definite portion of an area of low pressure with- 

 in which the conditions for the development of tornadoes are most favour- 

 able, and this is called the dangerous octant. 



2. That there is a definite relation between the position of tornado 

 regions and the region of high contrasts in temperature, the former lying 

 to the south and east. 



3. That there is a similar definite relation of position of tornado 

 regions and the region of high contrasts in the dew point, the former 

 being, as before, to the south and east. 



4. That the position of tornado regions is to the south and cast of 

 the region of high contrasts of cool northerly and warm southerly winds, 

 a condition that appears to be dependent upon the preceding, and is of 

 use when observations of temperature and dew point are not accessible. 



5. The relation of tornado regions to the movement of upper and 

 lower clouds presents some interesting points for study, but, as yet, no 

 decided results. 



6. The study of the relation of tornado regions to the form of 

 barometric depressions appears to show, that tornadoes are more frequent 

 when the major axes of the barometric troughs trend north and south 

 or north-east and south-west, than when they trend east and west." 



* In sach papers as Professional Papers of the Signal Service War Department. 

 No. IV. Tornadoes of May 20th and 30th, 1879. No. VI. Kcport on the character 

 of 600 tornadoes. No. XVI. Tornado Studiets for 1884. 



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