IT is not always the greatest inventions, or those which come most prominently before the public, which effect the greatest revolutions in the field of practical science; it is often the perfecting of_ instruments that have been long in use which is chiefly responsible for progressive results of startling significance. For instance, in the scientific researches oi chemical investigators, or in matters relating to pathology and meteorology, it is seldom that a fresh discovery is due to the invention of a new instrument; it is almost invariably the development of the power of assisting observation already existing in the old instruments which has effected new discoveries. This is peculiarly the case with modern instruments used in connection with geodetic work. It is the perfection with which the metal arc can now be graduated with equal divisions representing degrees, minutes, and seconds which has so greatly altered the conditions under which geodetic triangulation can be extended. The improvements effected in base measuring apparatus is another factor in the rapid evolution of earth measurement and map-making all over the world; whilst the improved pendulum for the registration of the varying force of gravity, corresponding to the varying conditions of density which obtain in the earth's crust, renders investigations into the science of isostasy more simple and more certain than could possibly have been anticipated, say, fifty years ago.