08 ANNUAL OF SCIENTIFIC DISCOVERT. 



Secondly, we have three models, which represent the most characteristic 

 and most widely distributed features of the ground. Having acquired from, 

 the preceding a thorough knowledge of fundamental principles, the pupil 

 will proceed to delineate upon paper the following models. These represent, 

 firstly, an undulating country; secondly, a plateau formation, with deeply- 

 cut valleys; thirdly and fourthly, some mountainous tracts. Contour lines 

 have been laid down upon the whole of these models with mathematical 

 accuracy. The horizontal projection of some of the most difficult sections 

 has also been added, to illustrate the manner of filling up the contour lines 

 and laying down auxiliary contours. It has not, however, been thought 

 advisable to do more, as otherwise the pupils would avail themselves of 

 these facilities to too great an extent. A small instrument for measuring 

 the gradients, and a scale showing the intensity of the shading (hachorres) 

 for various degrees of acclivity, are to be made use of in copying the models. 

 The author believes that the use of models, judiciously selected, will engage 

 the pupil's uninterrupted attention ; he will overcome mechanical difficulties 

 with greater facility, and will not be so wearied as by the tedious, but abor- 

 tive, and, in reality, useless attempts to copy a topographical drawing placed 

 before him. The author would add, that his models are made of galvano- 

 plastic copper, and are therefore not so liable to breakage as plaster-of-Paris 

 models. 



THE INDIA-RUBBER ARTIST. 



We have all of us laughed at the grotesque appearance made by toy heads 

 of vulcanized India-rubber. A little lateral pressure converts its physiog- 

 nomy into a broad grin, whilst a perpendicular pull gives the countenance 

 all the appearance that presents itself when we look into the bowl of a spoon 

 held longways. The pressure removed, the face returns to its normal con- 

 dition. Of the thousands of persons who have thus manipulated this play- 

 thing, it perhaps never struck one of them that in this perfect mobility lay 

 the germ of a very useful invention, destined to be, we believe, of great prac- 

 tical value in the arts. If we take a piece of sheet vulcanized India-rubber 

 and draw a face upon it, exactly the same result is obtained. This fact, it 

 appears, struck an observant person, and out of his observation has sprung 

 a patent process, worked by a company under the name of the "Electro 

 Printing-Block Company," for enlarging and diminishing at pleasure, to any 

 extent, all kinds of drawings and engravings. It must be evident that if a 

 piece of this material can be enlarged equally in all directions, the different 

 lines "of the drawing that is made upon it in a quiescent condition must' 

 maintain the same relative distance between each other in its extended 

 state, and be a mathematically correct amplification of the original draft. 

 The material used is a sheet of vulcanized India-rubber, prepared with a 

 surface to take lithographic ink; this is attached to a movable framework 

 of steel, which expands by means of very fine screws. On this prepared 

 surface lines are drawn at right angles; these are for the purposes of meas- 

 urement only. The picture to be enlarged is now printed upon its face in 

 the usual way; and supposing it is to be amplified four-fold, the screw 

 framework is stretched until one of the squares formed by the intersection 

 of the lines measures exactly four times the size it did while in a state of 

 rest. It is now lifted on to a lithographic stone, and printed, and from the 

 impression copies are worked off in the usual manner. If the picture has to 

 be worked with type, the enlarged impression has of course to be made 



