"The forms of the letters were probably invented at Serabit, in the isolation of the desert, by an illiterate people living in close contact with Egyptians. These people saw the Egyptian inscriptions being carved and thought they could do the same. There can be no doubt that this Sinaitic system is modelled on Egyptian, though not borrowed from it. [E.g., in my first study in 1916 I began by assuming that... was Eg. N, but soon found that this led to no result.] It was therefore highly intelligent imitation. That these intelligent illiterates invented the alphabetic principle is unlikely. It existed already to some extent in Egyptian beside the syllabic and ideographic principles. The "Sinaites" selected the alphabetic side of Egyptian writing (which was perhaps as much as they could understand) and applied it to their own (Semitic language. Probably if they had been more literary, i.e., had been really familiar with Egyptian writing, they would have contrived something much more elaborate. The system they adopted was (like that of the phonetic signs in Egyptian) consonantal and acrophonic, i.e., each sign was a picture which stood for the first letter of its name. Some of the signs chosen were Egyptian in form, but the values attached to them, being derived from the Semitic names of the objects represented, were not the same as the Egypt ian values. Thus ... is no doubt copied from the Eg. ... = h, but as it represents a house (semitic...) its value is b.
The values of the following 10 signs are now generally accepted, and are assumed here without discussion:"
From the Journal of Egyptian Archaeology, Volume XV, Parts 1-V, Pages 201-2. "The Sinaitic Inscriptions," by A.E. Cowley. 1929