394 General Notes. LJuly 



the Spring — the change in time being the result of a desire ex- 

 pressed by numerous members of the Union. 



After adjournment short field excursions were made in the 

 vicinity of Washington, April 9 and 10, by members of the 

 Union, under guidance of Prof. Cooke and Mr. E. A. Preble of the 

 Biological Survey. 



The next meeting of the Union will be held in San Francisco in 



May, 1915. 



John H. Sage, 



Secretary. 



GENERAL NOTES. 



A Misinterpretation. — While photography is in many instances the 

 only accurate and irrefutable means of determining the movements of 

 rapidly moving objects there appears to be a misinterpretation in connection 

 with the explanation of a figure in the April 'Auk.' I refer to the article, 

 " Does a grebe spread its wings just before diving? " by Mr. Verdi Burtch, 

 illustrated with Plates XXI and XXII. Figure 3, Plate XXI is a picture 

 of a diving grebe taken instantaneously at the moment of disappearance and, 

 as the author tells us, " shows a dark area representing the depression in the 

 water where the grebe sat at the begirming of the exposure, the ' ghost ' of 

 its wings fully spread out behind as it started to lunge forward and the 

 grebe itself nearly submerged a full length ahead." 



I conclude that the so-called ' ghost ' is considered to be ihe vague 

 photographic impression made at the very beginning of the exposure. The 

 shutter then remained open until the grebe had reached the almost sub- 

 merged position at the right. If the exposure had been of that duration a 

 continuous blurred image traversing the path taken by the grebe would 

 have been the inevitable result and not, as we have had it explained, " a 

 ' ghost ' of the wings " followed by a photographically undisturbed area 

 and then at the very close of the exposure a fairly well defined image of a 

 grebe diving with its head held erect. In any event the supposed " ghost 

 of the wings " would appear dark instead of Hght as seen in the figure on 

 Plate XXI and intensified in the enlargement. Why should the grebe 

 make such an intense and sharply defined image on the photographic plate 

 just as it is disappearing while during the first part of the exposure practi- 

 cally no impression was made? It might be argued that the impact with 

 the water had arrested its progress, but it does not seem possible that this 

 retardation can come so suddenly and be as great as the relative intensities 



