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Magnetic Observatory of the world. I t held an almost equally strong position in respect to the delicate pendulum apparatus by which the force of gravity is measured at different places on the globe, and again with regard to standard thermometers and meteorological instruments generally. Its Managers were eager to extend its operations to any kind of self-paying scientific experiment. Any person desirous of having a new invention tested could get it well done there at a cost that just repaid the trouble, subject, of course, to the permission of the Managing Committee and to the leisure of the staff.

One of the first things that I busied myself about, when I joined it, was to establish means for standardising sextants and other angular instruments. The cheaper kinds of these were unnecessarily bad, and many of the more costly were by no means so good as they should be for their price. I thought at first of utilising heliostats to give sharp points of reference by adjusting minute mirrors at distant points, flashing the sun on to them from larger mirrors at the Observatory, and using the return flashes as the points of reference. One of these small mirrors was fixed to the south obelisk, within a cage which may still be there. This arrangement was so far successful that beautiful stars of light were produced in response to flashes from the Observatory, but the uncertainty of sunshine in our climate showed the method to be of little practical value. Then Messrs. Cooke of York, who were among the foremost makers of large telescopes, devised an arrangement with collimators and artificial light. They made one for Kew, which is contained within a small dark room, and has acted