“You seem to be very adroit, Sir Clinton,” she observed. “But what is this about the length of my pace?”
“The inspector is accustomed to our English girls, madame, who have a free-swinging walk and therefore a fairly long step. From the length of the steps on the sand he inferred that they had been made by someone who was not very tall—rather under the average height. He forgot that some of you Parisians have a different gait—more restrained, more finished, shall we say?”
“Ah, now I see!” Mme. Laurent-Desrousseaux exclaimed, not at all unsusceptible to the turn of Sir Clinton's phrase. “You mean the difference between the cab-horse and the stepper?”
“Exactly,” Sir Clinton agreed with an impassive face.
Armadale was still puzzling over the two footprints. Mme. Laurent-Desrousseaux, evidently wearying of standing with one foot off the ground, recovered her shoe from him and slipped it on again. Sir Clinton took pity on his subordinate.
“Here's the explanation, inspector. When you walk in sand, you put down your heel first. But as the sand's soft, your heel goes forward and downward as you plant your foot. Then, as your body moves on, your foot begins to turn in the sand; and when you've come to the end of your step, your toe also is driven downwards; but instead of going forward, like your heel, it slips backward. The result is that in the impression the heel is too far forward, whilst the toe is in the rear of the true position—and that means an impression shorter than the normal. On the sand, your foot really pivots on the sole under the instep, instead of on heel and toe, as it does on hard ground. If you look at these impressions, you'll find quite a heap of sand under the point where the instep was; whilst the heel and toe are deeply marked owing to each of them pivoting on the centre of the shoe. See it?”
The inspector knelt down, and Wendover followed his example. They had no difficulty in seeing Sir Clinton's point.
“Of course,” the chief constable went on, “in the case of a woman's shoe, the thing is even more exaggerated owing to the height of the heel and the sharpness of the toe. Haven't you noticed, in tracks on the sand, how neat any woman's prints always look? You never seem to find the impression of a clumsy foot, simply because the impression is so much smaller than the real foot. Clear enough, isn't it?”
“You are most ingenious, Sir Clinton,” Mme. Laurent-Desrousseaux commented. “I am very glad indeed that I have not you against me.”
Sir Clinton turned the point.