This is illustrated by the _Stereoscope_, which consists of two mirrors placed each at an angle of 45 deg., or of two semi-lenses turned with their curved sides towards each other. To view its phenomena two pictures are obtained by the camera on photographic paper of any object in two positions, corresponding with the conditions of viewing it with the two eyes. By the mirrors on the lenses these dissimilar pictures are combined within the eye, and the vision of an actually solid object is produced from the pictures represented on a plane surface. Hence the name of the instrument, which signifies _Solid I see_.--_Hunt’s Poetry of Science._ PHOTO-GALVANIC ENGRAVING. That which was the chief aid of Niepce in the humblest dawn of the art, viz. to transform the photographic plate into a surface capable of being printed, is in the above process done by the coöperation of Electricity with Photography. This invention of M. Pretsch, of Vienna, differs from all other attempts for the same purpose in not operating upon the photographic tablet itself, and by discarding the usual means of varnishes and bitings-in. The process is simply this: A glass tablet is coated with gelatine diluted till it forms a jelly, and containing bi-chromate of potash, nitrate of silver, and iodide of potassium. Upon this, when dry, is placed face downwards a paper positive, through which the light, being allowed to fall, leaves upon the gelatine a representation of the print. It is then soaked in water; and while the parts acted upon by the light are comparatively unaffected by the fluid, the remainder of the jelly swells, and rising above the general surface, gives a picture in relief, resembling an ordinary engraving upon wood. Of this intaglio a cast is now taken in gutta-percha, to which the electro process in copper being applied, a plate or matrix is produced, bearing on it an exact repetition of the original positive picture. All that now remains to be done is to repeat the electro process; and the result is a copper-plate in the necessary relievo, of which it has been said nature furnished the materials and science the artist, the inferior workman being only needed to roll it through the press.--_Quarterly Review_, No. 202. SCIENCE OF THE SOAP-BUBBLE. Few of the minor ingenuities of mankind have amused so many individuals as the blowing of bubbles with soap-lather from the bowl of a tobacco-pipe; yet how few who in childhood’s careless hours have thus amused themselves, have in after-life become acquainted with the beautiful phenomena of light which the soap-bubble will enable us to illustrate!