I soon perceived that a lighthouse, whose number was continually repeated with a blink, obscuring just half its light, would be seen without any blink at all distances beyond half its range; but that at all distances within its half range that fact would be indicated by a blink. Thus with two blinks, properly adjusted, the distance of a vessel from a first-class light would be distinguished at from twenty to thirty miles by oc­cul­ta­tions indicating its number without any blink; between ten and twenty miles by an occultation with one blink, and within ten miles by an oc­cul­ta­tion with two blinks.

But another advantage was also suggested by this defect. {455} If the opaque cylinder which intercepts the light consists of two cylinders, A and B, connected together by rods: thus—

Such oc­cul­ta­tions are very distinct, and are specially applicable to lighthouses.

In the year 1851, during the Great Exhibition, the light I have described was exhibited from an upper window of my house in Dorset Street during many weeks. It had not passed unnoticed by foreigners, who frequently reminded me that they had passed my door when I was asleep by writing upon their card the number exhibited by the occulting light and dropping it into my letter-box.

About five or six weeks after its first appearance I received a letter from a friend of mine in the United States, expressing great interest about it, and inquiring whether its construction was a secret. My answer was, that I made no {456} secret of it, and would prepare and send him a short description of it.

I then prepared a description, of which I had a very few copies printed. I sent twelve of these to the proper authorities of the great maritime countries. Most of them were accompanied by a private note of my own to some person of influence with whom I happened to be acquainted.

One of these was addressed to the present Emperor of the French, then a member of their Representative Chamber. It was dated the 30th November, 1852. Three days after I read in the newspapers the account of the coup of December 2, and smiled at the inopportune time at which my letter had accidentally been forwarded. However, three days after I received from M. Mocquard the prettiest note, saying that he was commanded by the Prince President to thank me for the communication, and to assure me that the Prince was as much attached as ever to science, and should always continue to promote its cultivation.

〈EXPERIMENTS IN AMERICA.〉