Following numerous accidents, police ordinances have regulated the speed of motor vehicles, but their prescriptions are difficult to enforce. To impose the observation of imprudent drivers, it would be necessary, when the speed limit is exceeded, to be able to grasp the offense in some way on the fly and ascertain it indisputably.
Various means have been proposed, based on the use of instantaneous photography, but for the most part inapplicable. Here is a very practical one that does not require bulky devices or complicated calculations. It only requires a small, quite ordinary hand-held device with only one insignificant modification: the use of a shutter with two slits, unmasking the lens twice in succession, at a determined time interval. . The device provided with such a shutter will give on the plate two successive images which will be superimposed and merging if the objects are stationary, while, if they are moving, the two images will obviously be separated by the space traveled between them. both poses.
It is therefore sufficient to have any measurement of the vehicle, diameter or interval of the wheels to calculate the speed. However, these measurements are known for each type of car.
Here is the photograph of a teuf-teur ridden by two people and which descended the avenue des Champs-Elysées. To calculate how fast he walked, we only need two data: 1° the interval between the two poses - it was 4 hundredths of a second; 2° a dimension of the car - the distance between the two axles of this type of quadricycle is 1m.20.
These figures set, we proceed to the following operations: 1° we measure the reduction undergone on the test by the length of 1m.20 which separates the axles, and we find 2 cents. 25; 2° we make the proportion: 53.33; 3° this ratio is multiplied by the distance, measured on the test, between two positions of the same point on the car: 6 millimetres.
This multiplication gives the distance traveled in 4 hundredths of a second: 319 millim. 98. So the teuf-teuf walks at 7 meters 999 and a half millimeters per second, or 28 kilometers. 798 per hour.
The calculation is simpler to perform than to explain and to a very sufficient approximation, on the condition, however, that the car is represented exactly in profile and not in an oblique position, which would require the intervention of more complicated trigonometric considerations.
Our second photograph was taken with the same camera and the same shutter speed. Just looking at the images, we can see, without calculation, that the speed of this half-landau was more than half that of the quadricycle. The calculation gives indeed less than 14 kilometers per hour.
The ingenious device which we have just described was invented by M. Gaumont. Thanks to him, speeding can be recorded on the way by agents that nothing will report to careless drivers. These, warned, will no longer indulge in fantasies that impunity encouraged, and Mr. Gaumont will have deserved well from pedestrians and motorists themselves, who will no longer have adversaries when he no longer presents of danger.