It is desirable to place the barometer in such a position as not to be in danger of a side blow, and also sufficiently far from the deck above to allow for the spring of the metal arm in cases of sudden movements of the ship. If there is risk of the instrument striking anywhere when the vessel is much inclined, it will be desirable either to put some soft padding on that place, or to check movement in that direction by a light elastic cord; in fixing which, attention must be paid to have it acting only where risk of a blow begins, not interfering otherwise with the free swing of the instrument: a very light cord attached above, when possible, will be least likely to interfere injuriously. The vernier, as usual in standard barometers, reads to the two thousandth (.002) part of an inch. Every long line cut on the vernier corresponds to .01 part; each small division on the scale is .05; the hundredth parts on the vernier being added to the five when its lower edge is next above one of the short lines; or written down as shown by the figures on the vernier only, when next above one of the divisions marking tenths. In placing this barometer, it is only necessary to fix the instrument carefully, as indicated in the above directions, and give a few gentle taps with the fingers on the bottom, to move the mercury. Without further operation it will usually be ready for observation in less than an hour. When moving the barometer, or replacing it in its case, the mercury should be allowed to run gently up to the top of the tube, by holding the instrument for a few minutes inclined at an angle. The vernier should be brought down to the bottom of the scale. No other adjustment for portability is required. During carriage, it ought to be kept with the cistern end uppermost, or lying flat, the former position being preferable. If the mercury should not descend at first by a few gentle taps, use sharper (but of course without violence), by which, and two or three taps, with the finger ends, on the tube--between the scale and the tangent screw--the mercury will be made to begin to descend. In reading off from a barometer, it should hang freely, not inclined by holding, or even by touch. Sometimes, though rarely, at sea the mercury seems _stopped_. If so, take down the instrument (after _sloping_), reverse it, tap the tube gently while the cistern end is upwards, and then replace as before. * * * * * TESTING BAROMETERS, HYDROMETERS, AND THERMOMETERS.