Reproduction 47 
with the aid of a scale in my binocular. Of these three the last 
gave the most nearly accurate and most extensive results. 
The stop-watch method must take into consideration too many 
elements to be reliable. Thus, though the rate at which an 
object will fall in a vacuum is definite enough, the Lark is not 
in a vacuum. Furthermore it often has fallen considerably in 
altitude while singing before beginning the final drop and, fre- 
quently, it does not always fall directly down. However, a good 
many timings of the drop were made, the average of the whole 
being about five seconds. The bird thus, if in a vacuum, would 
have fallen, on the average, 496 feet. This, at least, gives an 
idea of the height but is greatly in error when air-friction and 
the lowering of altitude before the drop are considered. 
With one person to sight along the movable arm of a large 
levelled quadrant to secure the angle of a Lark in the air (but 
not directly overhead) and another to get directly beneath the 
Singing bird a triangulation could be secured. Thus, on one 
oceasion, this angle to the bird in the air plus the horizontal 
distance away were obtained. This is a simple trigonometric 
problem in which two angles and an included side are known. 
The result was about 350 feet. However this method is faulty, 
not in technique, but in execution. In the first place, two people 
are necessary to execute it; secondly, it is difficult to get to 
coincide the obtained angle and the horizontal distance at the 
Same time for the bird is constantly moving; lastly, a bird at 
maximum height cannot always be found with the unaided eye. 
With the binocular scale and the known length of the bird 
(about 8 inches or 19.0 cm.) estimation of height becomes rela- 
tively simple and accurate. It is necessary merely to find the 
value of a unit of the scale for the length of the bird at a known 
distance. The value of the scale unit for an object of known 
length at any distance can then be calculated from this known 
basis. It is merely a simple task of calibration. 
Thus, by using an old military binocular with an ocular scale, 
accurate measurements of the height of 25 song flights were ob- 
tained. The lowest noted was 270 feet, the highest 810 feet. 
The majority were delivered at about 540 feet. The average, 
Properly weighted, was 464.4 feet. 
Visibility of the Lark in flight song—The question of 
whether or not the Lark goes out of sight depends upon many 
