By JAMES GLAISHER, ESQ, F H.S. , THE variations in the readings of the barometer at the Royal Observatory, Greenwich, in the period from September 12 to November 30, making altogether eighty days, are shown in the accompanying diagram and table, together with the general directions of the wind on every day, as determined from the records of Osier's Self- Registering Anemometer, and the number of miles of horizontal movement of the air, as self-registered by the use of Robinson's Anemometer.

During the latter part of this period there have been successive heavy gales of wind upon our coasts, causing sad disasters at sea, and calling very frequently into use the services of the life-boats of the NATIONAL LIFE-BOAT INSTITUTION, and these, in most cases, have been attended with success in the saving of life; but unhappily in some few instances, as must ever be the case, the gales have been so violent that life has been lost; and the most noble efforts on the part of the life-boat crews, after toiling in some instances through the midnight storms, have failed entirely, the boats having been unable to reach the distressed ships.

A few particulars of the readings of the barometer during the period preceding these storms, and during their continuance, cannot fail to be useful and interesting to the brave men who are ever ready to go off in those life-boats, as well as to sailors and fishermen generally.

The readings of the barometer from the 1st of September to the 6th day were high, and above the average. On the 7th day it decreased a little below the average; on the 8th the lowest reading in the month took place, viz., 29'76 inches; and from the 9th day it was constantly above the average to the end of the month, being mostly above 30 inches, as shown in the diagram. The weather was exceedingly fine throughout the month. The highest reading in the month took place on the 23rd.There was a little decrease in the readings at the beginning of October; but on the 3rd day the reading again rose above 30 inches, and began to decline on the 5th, continuing to decrease till the 11th. Up to the 10th day the air had been mostly calm, and fog had been prevalent, but on this day the wind began to blow strongly from the W. and S.W. On the 11th the readings began to increase, and from the 12th the winds were light. A maximum barometer reading was reached on the evening of the 15th day. During the 16th the barometer readings decreased rapidly, and the wind increased in strength. A minimum reading of 28'89 inches was reached by 9 P.M. on the 18th, with strong wind blowing.

Unsettled weather followed this, and the barometer readings oscillated up and down, as will be seen by reference to the diagram, and the wind was frequently very strong, reaching 20 Ibs. on the square foot on the 25th day. From this time to the end of the month, the oscillations of the barometer readings were very remarkable; a decrease of J of an inch was followed by ah increase to the like amount; and then in very unusually quick succession, another decrease and increase to almost the same amounts, these very large and rapid changes extending over very considerable tracts of country and sea. The large numbers at the bottom of the table on those days will show how strongly the wind was blowing.

From this time there is a general bold and continuous increase in the barometer curve to 30J inches on the 12th of November, with mostly N. and N.E. winds blowing, and sometimes strongly. From the 13th day set in decreasing readings, which with checks, as shown in the diagram, fell to 28-82 inches on the 22nd day. At Liverpool Observatory, on this day, the reading was as low as 28-31 inches, as recorded by JOHN HARTNUP, Esq., the Director of the Observatory; and from this time to the 28th day, there was-a succession of disastrous storms, some of the effects of which will probably be detailed in other parts of the Life-boat Journal.

If we collate the numbers in the lower part of the chart together with different readings of the barometer, we shall find that when, the readings exceed 30 inches, the average daily Horizontal Movement of the air was about 130 miles per day; about 30 „ ditto 160 „ between 29-5 £30-0 in. ditto 210 „ „ 29-0& 29-5 in. ditto 260 „ below 29 inches ditto 320 „ -.-"- Thus showing that whenever the barometer reading has been above the average, the wind has been moderate, and that as the barometer reading decreases, the motion of the wind increases, and is the greatest at the lowest readings.

It is impossible for me to urge too strongly the necessity of care when continuous declining readings are proceeding.

The barometer may be almost neglected by the sailor when its readings range above the average; but when they descend below the average, it is a warning which ought never to pass unheeded; and when the depression is sudden, it is the sure and certain warning of the approach of storms. Such signs no sailor ought to neglect: yet they are neglected; and what is more sad still, too many barometers sold as marine barometers are totally unfit for such an important purpose. During the last few years I have seen many of these instruments, and I have found them imperfect in numerous ways. Some of these defects I may enumerate here:— Firstly.—The upper portion of the tube is too small.

Secondly.—The relation of the interior bore of the tube to that of the cistern is neglected, so that the rise of the mercury in the cistern, caused by a fall in the tube, is not allowed for on the scale.

Thirdly.—The lower portion of the tube is generally too much contracted in the bore.

Fourthly.—The cistern is too small to contain the mercury when the barometer reading is low.

Fifthly.—The careless cleaning out of the internal bore of the tubes, and imperfectly freeing them from damp.

The most serious of these errors is the third. It is well known that the tubes of marine barometers ought to have their bores contracted so as to steady the motion of the mercury when the ship is in a heavy sea.

This, in some instances, is so carelessly done, that it has not the desired effect; but in most cases it is carried to a great excess.

For instance, in some instruments the mercury will take from forty minutes to an hour to pass through the first inch after suspension, and many are so sluggish in their action as not to indicate any change in less than twenty minutes.

This unnecessary contraction is very frequently the cause" of entirely stopping the action of the barometer, as the minutest particle of foreign matter, or even the oxidation of the mercury itself, which, as an impalpable powder forming on the surface of the mercury in the cistern on moving the barometer, is displaced, and this in its ascent to float on the top of the mercury, chokes and closes the fine bore of the tube hermetically, rendering the instrument perfectly useless ; and this is often not found out till the ship has left for sea. A barometer, therefore, acting well till disturbed, may be quite useless afterwards.

The fourth-named error is also one of great gravity; and for this error low-priced manufacturers are far more to be censured for their culpability than for their ignorance or carelessness—the size of the cistern is reduced to enable them to save a quarter of a pound of mercury. This great desire to cheapen instruments is most serious, as the indications of such instruments are absolutely deceiving, and at a time when the changes are of vital importance to the sailor.

In many such barometers the mercury will not fall below, even if so low, as 29 inches, although a standard at such times may read 28 • 5 inches, or even less. Nor will such an instrument show any change till the mercury rises above 29 inches; that is, the barometer says the mercury is stationary and steady at all times of the greatest phases of storms, and when every change should be instantly known by the sailor.

It is therefore not to be wondered at that some master-mariners hold the barometer in little esteem if supplied with instruments of this class. Mr. PASTORELLI told me that he heard a captain say that he had the barometer removed, as it occupied some valuable space which was required for another purpose, and on arriving in the Port of Liverpool, that very instrument was found broken in an obscure nook of the ship. This is a sad illustration, and proves the absolute necessity of improvement in the make of these instruments. By using large cisterns, tubes of proper capacity, scales which are known as contracted scales, chemically clean tubes, pure mercury, and properly-contracted bores, instruments can be made which shall read within O'Ol or 0' 02 inch at every part of their scales, when compared with a standard barometer, and they ought to, and can be sold at a moderate price.

The contraction of the tube in a marine barometer ought to be carried only so far as to allow the utmost freedom of action of the mercury without pumping.

When the ship is in a heavy sea,—when first suspended,—the screw at the bottom of the tube being withdrawn as far as possible, —the mercury should fall in the tube through the first inch in 40 seconds to 60 seconds. It should fall through the second inch in less than two minutes, and should be at its true reading within or about 15 minutes from the time of first suspension.

Such an instrument, however quickly atmospheric changes may be taking place, will take up its true readings within 0 01 in. within one or two minutes, and this degree of accuracy is practically correct.

On removing such an instrument before packing, it should be taken down without touching the screw.at the bottom, and inclined with its cistern downwards, at an angle of 45° to 60° ; the tube will be filled in this position in three or four minutes; then hold the instrument horizontally, and drive the screw at the bottom nearly, but not quite, home. With these precautions, the instrument will continue good for many years—in fact, till broken. During the last few months I have had frequent interviews with Mr. JOHN BROWNING, of 111 Minories; Mr. F. PASTORELLI, of 208 Piccadilly ; and Mr. ZAMBEA, of 1 Hatton Garden, who have undertaken to make marine and upright barometers of this character for my examination ; and I have also undertaken to examine every one made by these makers, and to give a certificate with every instrument which complies with the above conditions. This will, I think, effectually meet the difficulty to which I have referred.

I feel confident that if our seamen had been provided with truthful instruments during the fearful storms of Wednesday the 22nd November last, and on the Friday following—the storms of those two days and nights would not have proved so disastrous as they did to life and property.

In corroboration of my remarks, I may mention one or two cases. Some four or five years ago Her Majesty's steamer Porcupine was cruizing off St. Kilda, in the Hebrides. Captain OTTER, R.N., carefully observing the gradual fall of the mercury to the extent of 1J inch between 8 A.M. on one day and 3'26 A.M. on the following day,* at once ordered his ship to be made as snug and tight as possible. The hurricane at the latter hour burst out with fearful violence, swept off' the little island nearly the whole of the agricultural produce of the poor people, and caused lamentable havoc amongst the shipping and fishingboats that happened to be out in those seas at the time. But the Porcupine weathered out nobly the storm; and in lieu of being in a thousand pieces, the good ship was engaged a few days afterwards in a mission of mercy in bringing food to the poor islanders.

I am sure that every assistance will be cheerfully rendered by the NATIONAL LIFE- * The following account of the reading of the barometer on the occasion in question cannot fail to be interesting, as showing clearly the certainty by which coming weather is indicated by this valuable instrument:— 1860 Inches.

October 2.—S -0 A.M., 30 • 32 8-0 P.M., 29-?5 8-15 P.M., 29-10 winds.

8 45 10-30 11-0 11-45 Octobers.—0-15 0-45 2-0 2-40 3-20 3-26 6-30 6-10 7-15 M., 29-62S.S.W.

M, 29-34SJ3.W.

M., 29-26 S.S.W.

K., 29-22 S.W.

M, 29 • 16 S.W. heavy squalls.

M., 29-10S.W.

.M, 23-96 S.W.

Ditto.

Ditto.

.«., 28-87 S.W. nearly calm.

M., 28-8t S.W. westerly.

N.W. hurricane began.

.M., 29-62 N., NJST.W. gale.

.M..29-65N.N.W.

.M., 29-55 N. nearly calm.

Koon 29-87 N.W. S.W. by S 2-30 P.M., 29-8 BOAT INSTITUTION to save life—whether by life-boats, ships' life-boats, seamen's life-belts, fishing life-boats ; or, lastly but not least, in its great and good work, by helping the sailor on board ship to possess a truthful and cheap barometer—a scheme which is indeed only an extension to the sea, of the coast barometer system of the Institution ; and thus prevent, as far as possible, by timely warnings on board ship, the necessity of calling into use the last but most glorious assistance—the services of the life-boat itself.

BlacMieath, December, 1865.