Laxey wheel, _380_, 381. Leads, 208. Lenses, 231; correction of for colour, 240, _241_; focus of, 236; rectilinear, _245_; spherical aberration in, 243. Levers, signal, colours of, 230. Speed governors, 67, _68_, _69_; Hartwell, 70; marine, 71. Speed of motor cars, 110. Spot, blind, in eye, 251; yellow, in eye, 251. Zech, Jacob, 414. Zeiss field-glasses, 260. THE END. APPENDIX. THE CRIMINALS OF THE SKY, & THE POLARISATION OF SKYLIGHT. 3. THE SKY.