, "but I think we will
take a wax mould of it."

He hurried downstairs, and, unstrapping the case from his bicycle,
brought it in and placed it on the table. As it was now getting dark, he
detached the powerful acetylene lamp from his machine, and, having
lighted it, proceeded to open the mysterious case. First he took from it
a small insufflator, or powder-blower, with which he blew a cloud of
light yellow powder over the table around the remains of the clock. The
powder settled on the table in an even coating, but when he blew at it
smartly with his breath, it cleared off, leaving, however, a number of
smeary impressions which stood out in strong yellow against the black
oilcloth. To one of these impressions he pointed significantly. It was
the print of a child's hand.

He next produced a small, portable microscope and some glass slides and
cover-slips, and having opened the paper and tipped the ball of fluff
from the key-barrel on to a slide, set to work with a pair of mounted
needles to tease it out into its component parts. Then he turned the
light of the lamp on to the microscope mirror and proceeded to examine
the specimen.

"A curious and instructive assortment this, Jervis," he remarked, with
his eye at the microscope: "woollen fibres--no cotton or linen; he is
careful of his health to have woollen pockets--and two hairs; very
curious ones, too. Just look at them, and observe the root bulbs."

I applied my eye to the microscope, and saw, among other things, two
hairs--originally white, but encrusted with a black, opaque, glistening
stain. The root bulbs, I noticed, were shrivelled and atrophied.

"But how on earth," I exclaimed, "did the hairs get into his pocket?"

"I think the hairs themselves answer that question," he replied, "when
considered with the other curios. The stain is obviously lead sulphide;
but what else do you see?"

"I see some particles of metal--a white metal apparently--and a number
of fragments of woody fibre and starch granules, but I don't recognize
the starch. It is not wheat-starch, nor rice, nor potato. Do you make
out what it is?"

[Illustration: FLUFF FROM KEY-BARREL, MAGNIFIED 77 DIAMETERS.]

Thorndyke chuckled. "Experientia does it," said he. "You will have,
Jervis, to study the minute properties of dust and dirt. Their
evidential value is immense. Let us have another look at that starch; it
is all alike, I suppose."

It was; and Thorndyke had just ascertained the fact