The instruments exhibited were especially fitted for working with the “messenger,” a perforated weight which is allowed to glide down the line or wire at a suitable interval behind the apparatus which it is to act on. The apparatus immediately acted on in this case is a trigger, or disengaging hook, of very simple construction, which is attached independently to the line above the principal apparatus. Separating the arrangement for freeing the apparatus (whether thermometer or water-bottle or other instrument) has many advantages. Being very light, it can be attached to the line by twine, or to the wire by a small clamp; and the principal apparatus can be attached in any convenient way, without it being necessary to pay minute attention to the knots or hitches that may be required. Further, in almost all cases, the principal apparatus and the separate trigger are much cheaper than the two combined. The separate trigger was exhibited attached to two forms of water-bottle for collecting water at intermediate depths. In one, which is a modification of a bottle for collecting bottom water, and is figured and described in the Challenger Reports, Narrative, vol. i. p. 117, the weights, which are provided to fall down and rest on the india-rubber valves K and H in the figure, are suspended by a line or wire to the trigger, and when the messenger falls on the trigger the line is slipped and the weights fall on the valves, which are then fixed, and enclose the sample. The pressure on the valves may be equally well produced by springs.