Two points are cited as illustrating the difficulty of enforcing the present regulations, namely, (a) the variation in the angle of the headlight beam caused by the compression of the springs when the loading of the car is changed from no load to full load and (b) the variation of the tilting of the beam caused by the pitching of the car on an ordinary road, the effect being similar to that produced by flashes of lightning in a pitch-dark night.
Denial is made of the author's alleged advocacy of diffused lighting and comparison is made of the distribution-curves obtained with frosted bulbs and those obtained with fairly good lamps conforming to the Society's specifications. Attention is called to three points in this comparison: (a) the light from the frosted bulb along the horizontal is only about 50 per cent of that available with a lamp conforming to the Society's specification, (b) the foot-candle illumination measured perpendicularly to the beam at various points on the surface of a level road is much less with the frosted bulb than with the lamp of the Society's specification, how much harm a bright illumination immediately in front of the car interferes with acuity of vision is a subject for additional research and (c) the light from the frosted bulb does not change appreciably for any angle through which the chassis is likely to move as a result of road shocks; consequently, when the frosted bulb is used, road shocks and spring vibration do not affect the eyes of an approaching driver.
Sharp cut-off above the horizontal is considered in-advisable. The possibilities of non-symmetrical lighting, the author believes, are worth considering, and the results of some experiments are detailed. He expresses a preference for the use of two diffused lights as regular equipment and of a third lamp, adjusted according to the Society's specifications, so that the maximum candlepower would be horizontal.
Reference is made to the test target in use by the Royal Automobile Club and to the results of tests made with it, but this method is said to be objectionable as a basis of specifications because it is tedious and the results depend largely upon the condition of the observer's eyes.
Although measurements of all the imaginable functions of the human eye have apparently been made, such tests should be repeated under automobile-lighting conditions, for factors that previously may have been neglected in tests frequently become important when the conditions are changed. As the normal eye requires nearly 1 sec. to adjust itself to radically changed conditions of illumination, this period is dangerously long when a car is running at high speed.