December 30, 1887.] 



SCIENCE 



325 



midnight of each day to the succeeding midnight. The following 

 table exhibits each prediction and the weather that followed ; — 



It will be seen that the prediction was the same in fifteen cases, 

 and eleven of these were fully verified. In order to obtain a fair 

 comparative estimate for the remaining ten days, the predictions 

 and the succeeding weather were referred to Prof. I. Russell, who 

 decided that No. (i) agreed better with the weather twice, and No. 

 (2) eight times. If these ten be regarded half verified, we shall 

 obtain for No. (i) 48 per cent and No. (2) 60 per cent. 



The predictions were also referred to Professor Upton, who sug- 

 gested two schemes for verification, by one of which he computed 

 No. (i) 67.2 per cent, and No. (2) 69.6 per cent; and by the other. 

 No. (I) had 61.0 per cent, and No. (2) 65.0 per cent. As Professor 

 Upton preferred the second scheme, I give it in detail. His plan 

 was as follows : — 



Arrange all possible weather-combinations in a table, and give 

 to each prediction a certain weight according to its position in the 

 table, as follows : — 



In this scheme it is possible that too much weight has been given 

 ' fair,' and too little ' threat.' However, as the prediction ' threat.' 

 seems of doubtful utility, it should have less weight. 



This discussion has brought out one fact of great interest regard- 

 ing methods of verification. Mr. Clayton verified the same predic- 

 tions by the observations at Blue Hill, a station very near Boston. 

 He makes the percentage 85. This great difference of 24 per cent 

 seems very surprising, and can hardly be due to the difference in 

 weather at the two places. It seems probable that this difference 

 is due to the method of verification, and that a mere percentage 

 obtained from an arbitrary verification cannot be relied on for com- 



paring the relative merits of two predictions. It is to be hoped 

 that a further discussion of this question may lead to clearer light 

 and understanding of the methods of prediction and verification 

 best suited to the needs of the public. H. A. Hazen. 



Washington, D.C., Dec. r4. 



The Chinese Wall. 



The note on the Chinese wall in a late issue of Science (x. No. 

 253), calling attention to Abb^ Larrieu's assertion that the wall 

 does not exist, recalled to mind Abb^ Hue's account. Turning to 

 it, I find that he was a believer in it, and with good reason. In Vol. 

 II. of his 'Journey through Tartary, Thibet, and China,' p. 31, he 

 gives the following account, which may interest some of your 

 readers, and serve to correct an erroneous impression : — • 



" The part of the wall immediately to the north of Pekin ... is 

 really fine and imposing; but it must not be supposed that this 

 barrier is equally large and solid throughout its whole extent. We 

 have had occasion to cross it at more than fifteen different points, 

 and have often travelled for days together without ever losing sight 

 of it ; and instead of the double battlemented stone wall which is seen 

 at Pekin, it is sometimes a very humble-looking wall of clay ; and 

 we have even seen it reduced to its simplest expression, and com- 

 posed only of stones piled up together." 



Thus, though the wall may not and does not have the magnitude 

 and solidity often attributed to it, yet in one form or another it cer- 

 tainly seems to exist, and is not, as we are told Abbe Larrieu says, 

 ' a huge Chinese lie.' Joseph F. James. 



Miami Univ., Oxford, O., Dec. 20. 



Tornado Force. 



I SEND you some facts in relation to tornado force and its pecul- 

 iarities of action, which may not be uninteresting to your readers, 

 on either side of the question, involving the nature of the force or 

 forces. 



The tracks examined by me did not present continuous lines of 

 destruction, but areas of destruction separated by intervals entirely 

 or almost entirely exempt from destructive forces, from which it is 

 inferred, that while the storm, in its common and ordinary features, 

 pursued its way steadily onward by bodily transferrence, the tor- 

 nadic action was developed interruptedly, and progressed by suc- 

 cessive transplantings. 



The first area examined, tornado of April 23, 1883, was composed 

 of two distinct parts. The first was a long rectangular space of 

 about half a mile in length, from west-south-west to east-north-east, 

 and a hundred and fifty to two hundred yards in width. Within 

 this space the trees were prostrated from south-east, south, south- 

 west, and west, and intermediate points ; and, wherever two or 

 more were found lying across each other, the one thrown from the 

 direction nearest to east, or farthest round from west,was always at the 

 bottom. Thus, those thrown from south always lay on top of those 

 from south-west, those from south-west on top of those from south 

 and south-east, and those from west were always on top of all other 

 directions. This order was without an exception. The rectangu- 

 lar area terminated at the east end in an irregularly circular area of 

 about eight hundred yards diameter, either east and west or north 

 and south. Bisecting this area both ways, and dividing it into four 

 quadrants, the south-west and south-east were found to correspond 

 in all respects with the rectangular area, except that in the south- 

 east there was a greater proportion of trees thrown down from 

 east-south-east and south-east than in the other sections ; and in 

 the south-west quadrant, near the centre, a tree thrown from south- 

 west was overlain by one from south, the single exception to the 

 order noted above. In the north-east quadrant the destruction was 

 less than in either of the others, and trees were thrown down from 

 east, north-east, north, north-west, and west. In the north-west 

 quadrant the trees were thrown from north, north-west, and west, 

 chiefly from north-west, west-north-west, and west ; and in the in- 

 stances where they crossed each other, the order in relation to the 

 west was similar precisely to that of the other parts, progressing 

 from east round by north to west, as, on the other side, the pro- 

 gression was from east round by south to west ; so that in these, 

 the north-east and north-west quadrants, trees thrown from north- 

 east lay under those from north, those from north under those from 



