RELATIVE STIMULATING EFFICIENCY OF LIGHT 147 



The candle power of the lamps used in the experiments was 

 measured by means of a Sharp-Millar photometer by Prof. H. 

 E. Howe of the Physics department of Cornell University, who 

 also approved the arrangement of the experiments. The- candle 

 power of the lamps used in the experiments described in sections 

 II, IV, VI, and VII was not measured until about a year after 

 the experiments were performed. During the interim they were 

 not used however and the depreciation due to age was probably 

 slight. 



III. ORIENTATION IN CONTINUOUS LIGHT FROM TWO SOURCES 



Since the object of the experiments described in this paper was 

 to ascertain the effect of intermittent light on orientation in 

 Vanessa it was first necessary to know the effect of continuous 

 light on orientation. This was ascertained in the following man- 

 ner. Two horizontal beams of light were arranged, as described 

 previously, so that they crossed at right angles. A sheet of 

 paper covered with soot from an oil lamp was placed in the field of 

 light common to the two beams, so that it was illuminated by 

 an equal amount of light energy from each of the sources. A but- 

 terfly with clipped wings was picked up in the fingers and gently 

 placed so that it faced a point about halfway between the two 

 sources, care being taken to avoid excessive stimulation by hand- 

 ling. The insect moved across the sheet of paper leaving a 

 trail in the soot. When it had completed this trial it was im- 

 mediately picked up, placed again at about the same starting 

 point, and allowed to complete another trial. In the same way 

 20 consecutive trials were given under these conditions. The 

 direction of the rays of light was then marked on the sheet, and 

 it was removed to be later coated with shellac, as described above. 

 Similarly the same individual was given 20 consecutive trials 

 with the relative illumination of the two beams of light in the 

 following ratios respectively, 3 to 4, 2 to 1, and 1 to 4. An in- 

 terval of at least thirty minutes separated each of the series of 

 tests under the above four different light conditions. Thirteen 

 butterflies were used, most of them being given all of the tests 

 described above. The results obtained are given in table 1. 



