'Whilst completing the model of my original plan,' he wrote to his mother on April 5, 'others on entirely fresh systems suggested themselves, and I have at length succeeded in combining the UTILE of each, but the mechanism requires a more delicate hand than mine to execute, or rather instruments which I do not possess. These I can readily have made for me in London, and by the aid of a lathe I shall he able to adapt the several parts, which I shall have made by different mechanicians for secrecy's sake. Should I succeed, it may be the means of putting some hundreds of pounds in my pocket. As it is a subject on which I was profoundly ignorant, until my attention was casually attracted to it the other day, I do not know what others may have done in the same way; this can best be learned in London.'

The 'fresh systems' referred to was his 'mechanical' telegraph, consisting of two letter dials, working synchronously, and on which particular letters of the message were indicated by means of an electro- magnet and detent. Before the end of March he invented the clock-work alarm, in which an electro-magnet attracted an armature of soft iron, and thus withdrew a detent, allowing the works to strike the alarm. This idea was suggested to him on March 17, 1836, while reading Mrs. Mary Somerville's 'Connexion of the Physical Sciences,' in travelling from Heidelberg to Frankfort.