The instrument mentioned is composed of a gutta percha globe, made in the manner previously described, into one end of which is inserted a tube of gutta percha or glass about four inches long, and at the opposite end of the ball is introduced a second tube about eight inches in length. To use this instrument, close the orifice of the longest tube, and plunge it into the water over any spot where the debris is collected, then by removing your finger from the end of the tube, _the impurity will be instantly sucked up into the ball_. By again placing the finger in its former position, the siphon may be lifted out of the tank, and its contents allowed to run off into a jug or basin placed near for the purpose. This operation must be repeated until the whole of the offending particles are removed. Of course, more water will be drawn off than is necessary, but it can easily be poured back into the tank as soon as the sediment has been fully precipitated. Aquaria are generally much more difficult to keep in order in summer than in winter, owing to the rapid and profuse growth of minute vegetation which renders the water opaque and exceedingly unpleasant to the eye. This ugly opacity I at one time attributed to decaying animal matter, for I could scarcely believe that the mere increase of the algæ spores could produce such a vile effect. Experience, however, has proved that the latter was in reality the true cause. I tried often by syringing the water, or drawing it off by means of the siphon, or stirring it about in all manner of ways, to remove the objectionable muddiness, but always without success. Limpets and Periwinkles seemed quite useless. Nor did shutting out the rays of light for a few days have any perceptible effect in subduing the growth of the algæ which collected with wondrous rapidity, and arrayed each stone, shell, pebble, and even the poor crabs, in a greenish garb. I was therefore under the necessity, on several occasions, of renewing the water, and considering that my residence was several miles from the sea-coast, this task was by no means a pleasant one. What made matters still more provoking, was the fact that the rejected fluid seemed perfectly free from all offensive smell. I now adopt the following novel method for removing the opacity of the water, without the latter being changed, and also for preventing the too abundant growth of the algæ at all seasons. The plan in question (which requires, as already shown, to be carried out with extreme caution by the inexperienced aquarianist) is merely to dilute a small quantity of _alum_ in a wine-glass full of water, and then mix it with the water contained in the aquarium. A pellet of alum about the size of a pea is sufficient for the purpose, if the tank be of moderate size. And if inserted on the first appearance of dimness in the water, much future trouble will be saved.