NATURE 



\July 20, 1882 



balance ; this rod hangs free, and is hit by a hammer, moved by 

 clockwork, at intervals of ten minutes. 



O'Reilly's is a balance barometer, but not at all similar to the 

 foregoing, as the cistern is fixed to the tube, and the instrument 

 is inclined from the vertical, and suspended by knife edges. The 

 variations in the length of the mercurial column cause it to 

 incline more or less, the amplitude of movement showing itself 

 on a graduated arc by means of an index. 



Cantoni employs a balance, but he has the tube fixed, and 

 suspends the cistern, which is a small one, from one arm of the 

 beam, to which is attached (underneath it) a pointer. Cecci 

 adopts the same principle, but traces the record on smoked 

 glazed paper (wound round a horizontal cylinder) by means of a 

 long pointer fixed over the beam. The floating barometer of 

 McGwire (Irish Acad. Trans, iv. 141, 179') ' s a balance baro- 

 meter, as its weight is counterpoised, or nearly so, by the 

 wooden ring attached to the botto.u of the tube. A very similar 

 instrument was patented by McNeill (Patent, No. 1733, 1861). 



Cistern Arrangements. — Prins maintained that by the following 

 arrangement he obtained a constant level in the cistern. The 

 reservoir has a glass cover a little below its rim ; this cover has 

 a hole in the centre rather larger than the tube which pas es 

 through it, through this space the mercury rises and • pre.nl 

 more or less over the cover. In Gloukhoff's barometer the 

 mercury in the cistern is forced by means of a screw to pass 

 through a hole, and to cover a glass ring. Then the movable 

 scale is lowered so as to make the steel end touch the surface of 

 the mercury. Amagat proposed to adjust the level in the cistern 

 by means of an iron or glass cylinder which was forced down by 

 a screw. Poleni (1740) adjusted the level by the immersion of 

 a screw. Austin (Roy. Irish Acad. Trans, iv., 99, 1 791) kept 

 the level of the mercury in the cistern constant by overflow 

 from an aperture in the side into a bag underneath. Hamilton 

 (Roy. Irish Acad. Trans, v., 95, 1792) fitted his barometer 

 with an ivory cistern, the upper part of which was 

 by a cork ring ; this being porous allowed air to pass 

 through, but retained the mercury. The cistern which is most 

 used is that of Fortin ; it is a short, wide, glass cylinder v. I 

 fixed by three pillars, the ends of which have screws 1 

 through an upper and a lower brass plate, by means of whic 

 necessary pressure can be applied to make it mercury-tight. At 

 the bottom of the cistern is a leather bag, which is r. 

 lowered by an adjusting screw, so that the surface of the mercury 

 may be brought into contact v. itli an ivory point which forms 

 the zero of the scale ; this point is seen through the glass cistern. 

 The cistern of Green's barometer, which is used by the Unite! 

 States Signal Service, is essentially the same as I 

 Negretti and Zambra (Patent, No. 238, lS6i) patented the 

 following. The cistern is screwed at the upper part to fittings 

 near the bottom of the tube, so that by turning it round it will 

 be raised until a cushion or pad placed at the bottom of the 

 cistern is brought up against the open end of the tube. Alver- 

 gnat {Rev. Hebd. d. Ckim. March 1S70) proposed a very elemen- 

 tary form on the same principle. Paul de Lamanon (" Obser- 

 vations sur la Physique," xix., 3, 17S2) in order to determine to 

 what extent the expansion of the mercury influenced the height 

 of the column, marked a zero point on the shorter limb of a 

 siphon barometer. Gay-Lussac (Ann. de Chim.i., 113, 1816), 

 who pointed out that, by having the tube of the same diameter 

 at both surfaces of the mercury, correction for capillarity was 

 unnecessary, also made his barometer portable by sealing the top 

 of the shorter limb with the exception of a very fine hole. 

 At the same time he made the lower portion of the longer 

 tube and the bend of tube of sufficiently small diameter 

 to keep the mercurial column from breaking. Bunten in- 

 troduced a great improvement by inserting an air-trap in the 

 barometer tube. This he effected by drawing off the lower 

 extremity of the upper half of the tube to form a capillary ; he 

 then sealed the lower half of the tube to the shoulder of the 

 contraction, so that any air accidentally entering the tube would 

 collect round this shoulder and not break the continuity of the 

 column or destroy the vacuum. Lefranc (Pogg. Ann. Ixxiv, 462, 

 1849) objected to Buntcn's tube as being very liable to fracture, 

 and proposed to guard against the admission of air by drawing 

 off the lower limb of the siphon to a capillary tube, and then 

 fitting to this tube by means of a perforated cork a short tube 

 which is, midway, contracted to a very small diameter. De 

 Luc used the siphon barometer, but made the instrument port- 

 able by inserting in the shorter limb an ivory stop-cock which 

 had a cork plug, but with a small ivory tube in the cork. 



Blondeau constructed a very similar instrument, but made it of 

 iron, and took his readings by means of a float. Stevenson's 

 is an iron siphon barometer provided with stop-cocks at 

 both limbs, so that it can be easily charged or emptied. 

 Bogen (Patent, No. 2532, 1877) patented the following barome- 

 ter : — The long leg of the siphon is closed at one end, and is 

 supplied with a glass stopper, with a fine hole through it, at the 

 other. The tube is filled, the stopper is inserted, and, the hole 

 through the stopper being closed by the finger, the tube is in- 

 verted and a portion of the mercury allowed to flow away to 

 produce a vacuum. The short leg is of the same diameter, and 

 is formed with a semicircular bend at one end, which is ground 

 to receive the open end of the long limb. The short limb is 

 then partly filled with mercury, the two parts are fitted together, 

 and the tube is brought to a vertical position. The level is read 

 off by the same method as that employed by Derham, but with 

 screw in place of rack and pinion. It stands on a centre, ;o 

 that by turning the instrument round it can be seen whether the 

 column is vertical. Greiner (Dove's Repert. d. J'hys. i., 31, 

 1837), 1835, drew the bend off to a capillary, which entered the 

 bottom of the open limb of the siphon. A short distance from 

 the bottom this tube is contracted, and when the barometer is 

 to be moved a plug is pressed into this contraction. W. Symons 

 (Patent, No. 813, 1S63) proposed to have no contraction, but to 

 make the plug close the capillary opening. Dorwin (Patent, 

 No. 13S6, 1S62) suggested a siphon barometer with cistern and 

 stopcock in place of open limb ; the cistern to be covered with 

 chamois leather, and the stopcock to have india-rubber connec- 

 tors above and below. Bohn constructs his instrument with 

 enlarged tubes at the two surfaces of the mercury ; the lower 

 one surmounted by a narrow tube for the purpose of filling, and 

 the upper one by a stopcock to facilitate the operation. 



Jas. T. Brown 



ON MONOSTROMA, A GENUS OF ALGAZ 



MOW that so much time and thought are devoted to the study 

 of the green algEE, Dr. Wittrock's ela igraph 



of the genus Monostrorna l will be f esirable addi- 



tion t<> our knowledge of these plants. The following abstract 

 work may therefore not be unacceptable 

 to the reader. 



In the Introduction Dr. Wittrock, who writes in Swedish, 



all that is known concerning the history of the formation 



of the genus, the discovery of the species, the changes which 



have taken place in the classification, and the works which treat 



of the subject. 



The genus Monostrorna was formerly included in Ulva, 

 Kiitzing was the first who divided the species of Ulva into 

 those which were formed of one layer of cells and those 

 which consisted of two layers. The former he called Ulva, 

 the latter Phycoseris. Thuret afterwards formed the species 

 with one layer into the new genus Monostrorna. According 

 to his arrangement Monostrorna is included in the second order 

 Zoospores?, sub-order, I, Chlorosporeae. 



Of the affinities of Monostrorna it will be sufficient to say 

 that, through the bladder-like form at an early period of growth 

 of two species, M. bullosum and M. Grevdlei, (the Ulva lachica 

 of Harvey), it approaches to Enteromorpha, from which it differs 

 in acquiring, at a later period, an expanded leaf like form, whereas 

 Enteromorpha always retains its tubular character. But a more 

 effective distinction is found in the structure of the frond, which 

 shows a nearer affinity with Tetraspora (which belongs to the 

 Palmellaceae). The chief distinction between Monostrorna and 

 Tetraspora lies in the zoospores, which, in M. bullosum, are (as 

 in the other Ulvaceae) oval, with the smaller end somewhat 

 drawn out into a kind of beak (rostrum), to which cilia are 

 attached. In Tetraspora the zoospores are nearly round, with- 

 out a rostrum, but with two long cilia fastened to the zoospores, 

 which can only be distinguished by their lighter colour. 



To Prasiola Monostrorna is also near. From this it is dis- 

 tinguished by the position of the cells, which are here never 

 arranged in quadratic or rectangular groups, and by the hold- 

 fast or root-organs. 



The frond (thallus) in Monostrorna, at least in mature specimens, 



is a flat, membranous expansion. In two of the species it is, when 



young, in the foim of a bladder or closed bag, which soon splits 



1 Firs, k till en Monographi Ofver AlgslSgtet Monostrorna, af V. B. 



Wittrock- Upsals, 1866. 



