A good self-registering tide-gauge is a valuable and important acquisition wherever tidal observations are required, and the only perfectly efficient instrument of this kind is that invented by the late Mr. John Newman, of Regent Street, London. It is now in action in several parts of the world, silently and _faithfully_ performing its duty, requiring no other kind of attention than that of a few minutes daily, and thus admitting the employment of the person on any other service whose duty it would otherwise have been to have registered the tide. It has done much by its faithful records in contributing to the construction of good tide tables for many places; for those unavoidable defects dependent on merely watching the surface on a divided scale are set aside by it, all erroneous conclusions excluded, and a true delineation of Nature's own making is preserved by it for the theorist. ADDENDA. 1. French barometers are graduated to millimetres. An English inch is equal to 25.39954 millimetres. Hence, 30 inches on the English barometer scales correspond to 762 millimetres on the French barometer scales. Conversions from one scale to another can be effected by the following formulae:-- (1) Inches = millimetres divided by 25.39954 (2) Millimetres = inches multiplied by 25.39954 Of course, a table of equivalent values should be drawn up and employed, when a large number of observations are to be converted from one scale to the other. 2. In Germany, barometers are sometimes graduated with old French inches and lines,--the vernier generally indicating the tenth of a line. OLD FRENCH LINEAL MEASURE. English Inches. 1 douzieme, or point = 0.0074 12 points = 1 ligne = 0.0888 12 lignes = 1 pouce = 1.065765 12 pouces = 1 pied = 12.7892 1 pied = 324.7 millimetres. "The Germans indicate inches by putting two accents after the number; lines, by putting three accents; 27" 3'''.85, means 27 inches 3 lines 85 hundredths of a line; more frequently, they give the height in lines, and the preceding number becomes 327'''.85."--_Kaemtz._ 3. _Rule for finding Diameter of Bore of a Barometer Tube._ "If the maker has not taken care to measure the interior diameter directly, it may be deduced from the exterior diameter. The exterior diameter is first measured by calipers, and, by deducting from this diameter 0.1 of an inch for tubes from .3 to .5 of an inch in external diameter, we have an approximation to the interior diameter of the tube."--_Kaemtz._ 4. WIND SCALES.