THE TORNADO OF 1851. 173 



facilitated. Having graduated two of the sides of a rigln-angled triangle to the proper 

 scale, one side is placed upon a cross line at the proper distance, and the other coordinate, 

 which is always less than a hundred feet, is read off at once, and the position of the 

 tree marked by a needle point, without drawing a single line. Each observer plotted 

 his own notes, on a scale of fifty feet to the inch. This large scale was adopted in order 

 to reduce the absolute errors as much as possible, and also to facilitate the detection of 

 any errors in the notes. The several sheets were then united, and a new map of the 

 whole made on a reduced scale of a hundred feet to the inch. 



It will be perceived, by a reference to the map, that the axis line of the survey is 

 represented by a heavy broken line. This line is not straight, but, in order to equalize 

 the length of the cross lines, offsets of a hundred feet or more were made in some places, 

 where it appeared that we were getting on one side or the other of the true axis of the 

 storm. After reaching the northern base of Wellington Hill, it will be perceived, also, 

 that the system above described is abandoned for a short time, while crossing a part of 

 the town of West Cambridge, and that the line is carried forward by courses running at 

 various angles. This method was adopted in order to avoid the well-cultivated gardens 

 of this particular district, where the encroachments of a surveying party, and the drag- 

 ging of chains through flower-beds might have aroused the apprehension of the several 

 proprietors. No inconvenience can arise from this, however, as, when once laid down 

 upon the map in its true bearing, it is easy for any one to overlook the axis of the survey, 

 and to mark out for himself the axis of the storm, as indicated by the traces which it has 

 left. 



A few words seem to be necessary, by way of explanation, of the frequent recurrence 

 of the symbol adopted to represent those trees which had been thrown down, but which 

 were replaced at the time of the survey. The storm occurred on the 22d of August. 

 At that time I was absent from Cambridge, and even had I been present, the survey 

 could not have been undertaken until the members of my class had reassembled, at the 

 end of the vacation. The survey was commenced on the 2d of September, and pros- 

 ecuted without interruption during a period of ten days, with a party varying from 

 twelve to thirty. As the storm passed over a section of country which is one of the 

 principal sources of supply for the Boston market, and therefore in a high state of culti- 

 vation, the farmers were the chief sufi'erers, many of them experiencing very severe 

 losses by the destruction of their orchards. Most of these trees were simply blown 

 down, with the roots on one side still clinging firmly to the ground, and the farmers with 

 great alacrity set themselves at work to replace them, supporting them temporarily with 

 shores. This work had been going on during the period of ten days which had elapsed 



