OCR Rendition - approximate

296 Mr. Francis Galton rampart ; it is of equal height throughout. A cut has been made at right angles to its base with a fret-saw, to divide it into two portions -that which would remain after it had been breached, Fig. 8, and the FIG. 9. 1877.] on Typical Laws of Heredity. 297 shallow frame, while those that came from the distant compartments will stand even lower than they did before. It follows that the selected pellets form, in the lower compartment, a heap of which the Fro. 11. [Feb. 9, cast of the breach. Then a second cut with the fret-saw has been made at right angles to its face, to out out of the rampart an equivalent to the heap of pellets that represents the original population. The gap that would be made in the heap and the cast that would, fill the gap are curved on two faces, as in the model. This is sufficiently represented in Fig. 10. FIG. 10. The operation of natural selection on a population already arranged according to the law of deviation is represented more completely in an apparatus, Fig. 11, which I will set to work immediately. It is faced with a sheet of glass. The heap, as shown in the upper compartment of the apparatus, is 3 inches in thickness, and the pellets rest on slides. Directly below the slides, and running from side to side of the apparatus, is a curved partition, which will separate the pellets as they fall upon it, into two portions, one that runs to waste at the back, and another that falls to the front, and forms a new heap. The curve of the partition is a curve of deviation. The shape of this heap is identical with the cast of the gap in Fig. 10. It is highest and thickest in the middle, and it fines away towards either extremity. When the slide upon which it rests is removed, the pellets run down an inclined plane that directs them into a frame of uniform and shallow depth. The pellets from the deep central compartments (it has been impossible to represent in the diagram as many of these as there were in the apparatus) will stand very high from the bottom of the scale of deviation is much more contracted than that of the heap from which it was derived. It is perfectly normal in shape, owing to an interesting theoretical property of the law of deviation (see formula at end of this memoir). Productiveness follows the same general law as survival, being a CIibPDF - www.fastio.com