Messrs Siemens’ improvements in the dynamo-electric machine appear likely to settle the question as regards transmission of mechanical power to long distances. Given the power to work one machine, it can be transmitted by wires to a second, from that to a third, and so on continuously through many miles. A waterfall or steam-engine of one hundred horse-power working the first machine in the series would produce fifty horse-power at a distance of thirty miles. Hence it would be possible to grind wheat, to shape iron in a lathe, to saw wood, or weave cotton by machinery, in a district where all the coal was exhausted. This consideration ought to be appreciated by the people who imagine that our coal-fields will all too soon be dug completely out. Another advantage of the dynamo-machine is that if thrown out of gear for a few minutes or for a longer time there is no loss or waste of power. Considering that slag can be made into glass, and that slag is a disagreeable encumbrance which many manufacturers would gladly get rid of, a suggestion has been offered that, instead of being made of metal, tanks and cisterns should be made of slag glass, in a single casting. There would then be no leaky joints, no unpleasant taste from paint or metal; cleaning would be easy; and if large dimensions were required, a number of small tanks might be placed side by side, and connected by slag-glass tubes. When this suggestion comes to be adopted, there will be no need to inquire about prevention of rust in tanks, nor to be timorous of lead-poisoning. Very tedious is the work of reducing tables of observations to their true value, whatever their nature. Observations of tides are no exception; and as their reduction is of great importance in working out a true theory of the tides, attempts have been made to accomplish the tedious task by machinery, and at length with success. Sir William Thomson, of the University of Glasgow, has now constructed what he calls an ‘harmonic analyser,’ with which he can work out the analyses of a twenty-four-hour tide-curve in about a minute. It is usual in taking tidal observations that the gauge records the rise and fall in the twenty-four hours in the form of a curve on a sheet or roll of paper; and the labour of analysing the sheets of a whole year may be imagined. But, as Sir W. Thomson’s machine will clear sixty or more sheets in an hour, a year’s work may be satisfactorily disposed of in half a day. This will indeed be good news to the able investigators who have for some years investigated the voluminous series of arctic tides, and are still far from completion. Their work will be greatly simplified; but the machine by which this happy result is achieved involves some of the most refined principles in natural philosophy.