Louis in 1871， which have suggested to him the true solution. Here isthe letter which I had this morning acknowledging my assistance.”
He tossed over， as he spoke， a crumpled sheet of foreignnotepaper. I glanced my eyes down it， catching a profusion ofnotes of admiration， with stray “magnifiques，” “coup-de-ma.tres，”
and “tours-de-force，” all testifying to the ardent admiration of theFrenchman.
“He speaks as a pupil to his master，” said I.
“Oh， he rates my assistance too highly，” said Sherlock Holmeslightly. “He has considerable gifts himself. He possesses two outof the three qualities necessary for the ideal detective. He has thepower of observation and that of deduction. He is only wanting inknowledge， and that may come in time. He is now translating mysmall works into French.”
“Your works？”
“Oh， didn’t you know？” he cried， laughing. “Yes， I have beenguilty of several monographs. They are all upon technical subjects.
Here， for example， is one ‘Upon the Distinction between theAshes of the Various Tobaccoes.’ In it I enumerate a hundred andforty forms of cigar， cigarette， and pipe tobacco， with coloredplates illustrating the difference in the ash. It is a point which iscontinually turning up in criminal trials， and which is sometimesof supreme importance as a clue. If you can say definitely， forexample， that some murder has been done by a man who wassmoking an Indian lunkah， it obviously narrows your field ofsearch. To the trained eye there is as much difference betweenthe black ash of a Trichinopoly and the white fluff of bird’s-eye asthere is between a cabbage and a potato.”
“You have an extraordinary genius for minutiae，” I remarked.
“I appreciate their importance. Here is my monograph uponthe tracing of footsteps， with some remarks upon the uses ofplaster of Paris as a preserver of impresses. Here， too， is a curiouslittle work upon the influence of a trade upon the form of thehand， with lithotypes of the hands of slaters， sailors， corkcutters，compositors， weavers， and diamond-polishers. That is a matter ofgreat practical interest to the scientific detective—especially incases of unclaimed bodies， or in discovering the antecedents ofcriminals. But I weary you with my hobby.”
“Not at all，” I answered earnestly. “It is of the greatest interestto me， especially since I have had the opportunity of observing yourpractical application of it. But you spoke just now of observationand deduction. Surely the one to some extent implies the other.”
“Why， hardly，” he answered， leaning back luxuriously in hisarmchair and sending up thick blue wreaths from his pipe.
“For example， observation shows me that you have been to theWigmore Street Post-Office this morning， but deduction lets meknow that when there you dispatched a telegram.”
“Right！” said I. “Right on both points！ But I confess that I don’tsee how you arrived at it. It was a sudden impulse upon my part，and I have mentioned it to no one.”
“It is simplicity itself，” he remarked， chuckling at my surprise—“so absurdly simple that an explanation is superfluous； and yet itmay serve to define the limits of observation and of deduction.
Observation tells me that you have a little reddish mould adheringto your instep. Just opposite the Seymour Street Office they havetaken up the pavement and thrown up some earth， which lies insuch a way that it is difficult to avoid treading in it in entering.
The earth is of this peculiar reddish tint which is found， as far as Iknow， nowhere else in the neighborhood. So much is observation.
The rest is deduction.”
“How， then， did you deduce the telegram？”
“Why， of course I knew that you had not written a letter， since Isat opposite to you all morning. I see also in your open desk therethat you have a sheet of stamps and a thick bundle of postcards.
What could you go into the post-office for， then， but to send awire？ Eliminate all other factors， and the one which remains mustbe the truth.”
“In this case it certainly is so，” I replied after a little thought. “Thething， however， is， as you say， of the simplest. Would you think meimpertinent if I were to put your theories to a more severe test？”
“On the contrary，” he answered， “it would prevent me fromtaking a second dose of cocaine. I should be delighted to look intoany problem which you might submit to me.”
“I have heard you say it is difficult for a man to have any objectin daily use without leaving the impress of his individuality uponit in such a way that a trained observer might read it. Now， Ihave here a watch which has recently come into my possession.
Would you have the kindness to let me have an opinion upon thecharacter or habits of the late owner？”
I handed him over the watch with some slight feeling ofamusement in my heart， for the test was， as I thought， an impossibleone， and I intended it as a lesson against the somewhat dogmatictone which he occasionally assumed. He balanced the watch inhis hand， gazed hard at the dial， opened the back， and examinedthe works， first with his naked eyes and then with a powerfulconvex lens. I could hardly keep from smiling at his crestfallenface when he finally snapped the case to and handed it back.
“There are hardly any data，” he remarked. “The watch has beenrecently cleaned， which robs me of my most suggestive facts.”
“You are right，” I answered. “It was cleaned before being sent tome.”
In my heart I accused my companion of putting forward a mostlame and impotent excuse to cover his failure. What data could heexpect from an uncleaned watch？
“Though unsatisfactory， my research has not been entirelybarren，” he observed， staring up at the ceiling with dreamy， lacklustreeyes. “Subject to your correction， I should judge that thewatch belonged to your elder brother， who inherited it from yourfather.”
“That you gather， no doubt， from the H. W. upon the back？”