“Do you mean that you still invent imaginary cases as mental exercises?”

“No; I mean that, when I have a problem of any intricacy, I invent a case which fits the facts and the assumed motives of one of the parties.  Then I work at that case until I find whether it leads to elucidation or to some fundamental disagreement.  In the latter case I reject it and begin the process over again.”

“Doesn’t that method sometimes involve a good deal of wasted time and energy?” I asked.

“No; because each time that you fail to establish a given case, you exclude a particular explanation of the facts and narrow down the field of inquiry.  By repeating the process, you are bound, in the end, to arrive at an imaginary case which fits all the facts.  Then your imaginary case is the real case and the problem is solved.  Let me recommend you to give the method a trial.”

I promised to do so, though with no very lively expectations as to the result, and with this, the subject was allowed, for the present, to drop.

Chapter XII

The Portrait

The state of mind which Thorndyke had advised me to cultivate was one that did not come easily.  However much I endeavoured to shuffle the facts of the Blackmore case, there was one which inevitably turned up on the top of the pack.  The circumstances surrounding the execution of Jeffrey Blackmore’s will intruded into all my cogitations on the subject with hopeless persistency.  That scene in the porter’s lodge was to me what King Charles’s head was to poor Mr. Dick.  In the midst of my praiseworthy efforts to construct some intelligible scheme of the case, it would make its appearance and reduce my mind to instant chaos.

For the next few days, Thorndyke was very much occupied with one or two civil cases, which kept him in court during the whole of the sitting; and when he came home, he seemed indisposed to talk on professional topics.  Meanwhile, Polton worked steadily at the photographs of the signatures, and, with a view to gaining experience, I assisted him and watched his methods.

In the present case, the signatures were enlarged from their original dimensions—­rather less than an inch and a half in length—­to a length of four and a half inches; which rendered all the little peculiarities of the handwriting surprisingly distinct and conspicuous.  Each signature was eventually mounted on a slip of card bearing a number and the date of the cheque from which it was taken, so that it was possible to place any two signatures together for comparison.  I looked over the whole series and very carefully compared those which showed any differences, but without discovering anything more than might have been expected in view of Mr. Britton’s statement.  There were some trifling variations, but they were all very much alike, and no one could doubt, on looking at them, that they were all written by the same hand.