382 



THE NATIONAL GEOGRAPHIC MAGAZINE 



ever, it could not account for more than 

 a portion of the great difference. 



This result is from the examination of 

 ten specimens that in the aggregate 

 weighed 674 milligrams. 



WING rate;s of^ powere'ul insect fliers 



Records of wing vibrations ot a speci- 

 men of Syrphus that had been in cap- 

 tivity 24 hours, and meanwhile fed on 

 sugar and water, gave, as the average of 

 four tests, 400 per second. The voice of 

 this fly when scared by pressure varied 

 from violin A to the C above. 



A second specimen gave 378 as the 

 average of five tests. One test in the 

 same quarter-second gave 341 and 578, 

 the slower being at the beginning of an 

 eflfort, the faster at the maximum speed 

 attained. These rates, which at first ap- 

 peared to be the true wing rates, proved 

 ultimately to be subsidiary vibrations. 



Wing vibrations of Volucella, 298, 

 average of six tests. The tests varied 

 remarkably, being as follows : 228, 253, 

 275, 282, 348, 405. The latter two are 

 remarkably above the others, and are 

 subsidiary vibrations. 



Three tests on a green-bottle fly gave 

 250, 258, 196. Average, 235. 



A large sarcophagous fly, female, as 

 the result of seven tests, gave an average 

 of 246 per second. In the course of these 

 tests rates as high a,; 400 were observed 

 for short periods of time, but these were 

 probably subsidiary vibrations. The tests 

 ran as follows: 199, 206, 227, 257, 268, 

 281, 281. 



The wing vibrations of one of the 

 large sarcophagous flies held captive, on 

 being chronographed, gave as the result 

 of seven different trials 203 vibrations 

 per second. 



Golden dragon fly {Pantala Havescens, 

 Fab.), 17 per second, five observations, 

 one individual. 



Large dragon fly {Arax Junius, 

 Drury), 22 per second, seven observa- 

 tions, one individual. 



Tuning-fork tests on the same paper 

 as the above tests gave results as fol- 

 lows : Pitch, A international. 420, 446, 

 462. Average, 443. 



HIGH WING-RATE FEIERS VS. THE SAILERS 



The dragon flies are well known to be 

 powerful fliers. Nearly everybody must 

 have noticed the bold flight of these con- 

 spicuous insects, which may at times be 

 seen soaring high above the roofs of 

 houses in our towns, and even over the 

 tops of some of our high hills and moun- 

 tains. We may, therefore, arrive at a- 

 more accurate conception of the flight of 

 flies if we compare it with that of these 

 larger insects which come under more 

 common observation. 



The relative powers of flight of the fly 

 Volucella obesa and the large dragon fly 

 is shown by the usually futile attempts 

 of the latter to capture the former. I 

 have never seen a Volucella captured by 

 one of these dragon flies, though the 

 Volucella when standing still in the air 

 offers an unusually fair mark. When, 

 the dragon fly arrives the Volucella is 

 gone. The fact that dragon flies con- 

 tinue to make passes at them may indi- 

 cate that the flies are sometimes caught. 



A golden dragon fly and a Volucella, 

 whose weight were to each other as 297.4 

 to 64.2 (mg.), had wing areas that were 

 to each other as 46.8 to 1.6. 



Or, to speak approximately, a dragoni 

 fly weighing only four to five times as- 

 much as a fly, both being expert fliers of 

 their respective kinds, had a wing area 

 thirty times as great. 



A Volucella fly and a large dragon fly,, 

 whose weights were to each other as 64.2' 

 to 1598.5 (mg.), had wing areas that 

 were to each other as 1.6 to 82. ; that is- 

 to say, speaking approximately, the 

 dragon fly, while she weighed only 25 

 times as much, had a wing area over 50 

 times as great. 



A REMARKABLE ELIGHT 



I remember once to have witnessed a 

 very remarkable example of the power 

 of flight of one of the larger flies. On a 

 voyage across the Mediterranean from 

 Algiers to Marseilles in company with 

 Prof. W. T. Swingle, I observed a dip- 

 terous insect keeping pace with the 

 steamer so accurately that it almost 

 seemed as if it were joined to the boat 



