Presently, after they have been finished off, the models are towed through the tank, and their resistance is measured by a dynamometer, the automatic drum simultaneously measuring the course and time. It should be mentioned that it is after the models have been formed in sifted clay that they are cast in wax as a hollow shell, the core being made of battens, strong canvas being also employed. After the model has been subjected to the cutting machine, it is planed and scraped by hand to remove the excrescences of paraffin. The advantage which the experiments made in tanks give lies in the fact that one can thereby ascertain the resistance which the model will encounter through the water, and consequently the amount of effective horse-power that she will require. Granted that an owner desires to have built a steamship of a certain displacement, it follows that that amount of displacement is capable of being embodied in numerous different shapes; and it is part of the work of the experimental tank to determine the most suitable ratios of length, breadth and draught which shall produce the ideal ship for the purpose desired. Indeed, it may be said that it is only by means of the experiments made in tanks that any safe and reliable method can be afforded for attaining the desired end. The model is made according to scale with a displacement proportionate to that of the steamship to be built, and the correct amount of immersion is given to the model by adding ballast in the shape of small linen bags containing shot. In order to obtain the measurements of the model’s resistance in the water, it is placed under the carriage which bears the measuring instruments for indicating both the resistance of the model, and the thrusting and twisting stresses of the model screws. It should be explained that the carriage is moved by motors which derive their current from accumulators, and it is possible, by regulating the accumulators, to obtain over 400 different speeds. The advantage of this in studying the wave formation which the models set up is of the highest importance. To be able to ascertain how much resistance the model sets up at lesser and higher speeds is a great gain, and in no respect is this information more valuable than when experiments are being made with a view to high-speed torpedo boats; but as this kind of craft does not come within our present scope, we must pass on.