An elaborate and very lucid article on the Electrotype and Daguerreotype, being a review of “An Account of Experiments in Electricity made by Thomas Spencer--Annals of Electricity, January 1840,” and of the account of M. Daguerre’s discovery of Photogenic Drawing as published by himself, has appeared in that excellent work “The Westminster Review” for September. Our space not allowing us to enter so fully into details as our admirable contemporary, we present our readers with as concise an article as the nature of the subject will permit, confining ourselves for the present to the Electrotype, as being less generally known, though not less curious. The electrotype is another instance of the application of invisible elements to the uses of man, by which powers and influences, of whose nature he is as yet wholly ignorant, are made subservient to his purposes, and obedient to his rule. To define accurately what electricity is, would be, as yet at least, impossible. Many conjectures have been, are, and will be hazarded, but the knowledge of its production, power, and effects, is only in its infancy, and so full of promise of a gigantic growth, that time will be better spent in its cultivation than in debating upon what it is. The truth of this proposition is fully borne out by the subject of our present paper; for whilst many scientific men have been exhausting their energies in the production of plausible theories upon the nature of the electric fluid, other more matter-of-fact philosophers have addressed themselves to its application; and whilst some of these devote themselves to the developement of its motive powers, in the well-founded hope of its superseding steam, others press its services to far different uses. Amongst the last, Mr Spencer holds a foremost place. Before entering into the description of the electrotype, we must say a few words on the subject of electricity to the less informed of our readers. The electric fluid, as it is called, may be produced in various ways: the most ordinary is by the friction of glass against silk, as exemplified in the electrical machine, which is familiar to almost every one. But galvanic and voltaic electricity is differently produced. In all cases its production is the consequence of combination, but particularly in the galvanic battery and voltaic circle. The latter, being Mr Spencer’s apparatus, we shall briefly describe.