NATURE 



\_March 27, 1879 



tylopora, and Uteria. This group at present contains 

 over fifty genera, which are for the most part to be met 

 ■with in the triassic, Jurassic, cretaceous, and tertiary 

 strata. In the number of those actually living there is a 

 notable falling off, there being not more than the seven 

 following genera : — Dasycladus, Halicoryne, Cymopolia 



Fig. I. — Transverpe tect.on of a morsel cf the calcareous tube cf Cj tticfclia 

 rosarzutn, Lamr., shcwirg the canals which receive the whcrl cf cel- 

 lules and the central spcrangial cavity. FiG. 2. — TiantverEe secticn of 

 Polytryfa elcngata, Defiar.ce, ?htwing the sr.me forticr.s. Fig. 3. — 

 Part of a whorl cf cellules of C}7tufoiia 7csaru.ni, sepaiaied ficm the 

 calcareous tube by acid. A, wall ot cer.tial cellule ; B, frst row cf cel- 

 lules ; c, terminal whcrl cf cellules, in the centre of which is D, the 

 axillary sporangium. Fig. 4.— Exactly the same parts in Polytrypa 

 elofigata, obtained Ircm a mculd. 



(with two sub-genera, Polytrypa and Decaisnella,i g.n.), 

 Polyphysa, Acetabularia, Neomeris, and Bornetella,* g.n." 

 [Doubtless a few more genera of recent forms yet remain 

 to be described. Thus Chloroclados, of Sonder, appears 

 to be a good and distinct genus allied to Dasycladus.] 



"The frond in the Siphoiiece verticillatcE is simple or 

 dichotomous ; it consists of a central tubular unicellular 

 axis, around which are arranged the radiary and verticel- 

 late ramuli, the exact arrangement of which varies accord- 

 ing to the genera and to the species. In most of the 

 species carbonate of lime is found deposited in abundance 

 in the outer walls of the main axis and its ramuli, and 

 this forms around the plant a calcareous envelope, in 

 which is reproduced all the details of its organisation. 

 This mineral coating may consist of one or of two cal- 

 careous cylinders. The inner cylinder will be formed by 

 the central axis, and the first row of cells which arise 

 therefrom. The outer cylinder is laid down by the most 

 external of the verticels of cells ; these terminate by a 

 splayed-out enlargement, the lateral edges of which be- 

 come more or less consolidated with the similar enlarge- 

 ments of neighbouring cells, and by thus causing a reci- 

 procal pressure, very regular hexagonal surface markings 

 are produced. The organs of fructification are themselves 

 surrounded by calcareous material, and assist in the 

 formation of the outer cylinder, a fact easily seen in any 

 section of Cymopolia." 



The result of such an organisation is that when the 

 organic vegetable matter becomes destroyed there still 

 remains in those fossil species, which laid down a great 

 deal of calcareous material, as well as in those living 

 species — which lay down more or less of it — a skeleton 

 permeated by canals (rays of the ramuli) and chambers 

 (fructification). This arrangement, which permits of an 

 exact classification of the fossil species, being wrongly 

 interpreted, led even some most distinguished authors to 

 see in these morsels of plants the full organisation of a 

 Foraminifer." 



Space will not permit of the table of the twenty-two 

 genera and seven families as detailed in the ComptesRoidits 



' Type, Dactylofiora eriica, Paiker. 

 " type, Neemtris nitida, Harv. MS. 



being here given, but every botanist will look forward 

 with interest to the promised future detailed contributions 

 of the author on this subject. Here it seems desirable to 

 add that his conclusions are in every particular acquiesced 

 in by one in every way thoroughly able to judge of 

 the facts, Dr. Ed. Bornet, and having written this I 

 feel it almost superfluous to say that on a careful study 

 myself of specimens prepared by M. Munier-Chalmas — 

 for which I take this opportunity of thanking him— I cannot 

 conceive his demonstration as admitting of a doubt, 



Ed. Perceval Wright 



ELECTRICITY AND WATER DROPS i 



T T has been known for many years that electricity has 

 ■■■ an extraordinary influence upon the behaviour of fine 

 jets of water ascending in a nearly vertical direction. In 

 its normal state a jet resolves itself into drops, which even 

 before passing the summit, and still more after passing it, 

 are scattered through a considerable width. When a 

 feebly electrified body is brought into its neighbourhood, 

 the jet undergoes a remarkable transformation, and 

 appears to become coherent ; but under more powerful 

 electrical action the scattering becomes even greater than 

 at first. The second effect is readily attributed to the 

 mutual repulsion of the electrified drops, but the action of 

 feeble electricity in producing apparent coherence has 

 been a mystery hitherto. 



It has been shown by Beetz that the coherence is ap- 

 parent only, and that the place where the jet breaks into 

 drops is not perceptibly shifted by the electricity. By 

 screening various parts with metallic plates, Beetz further 

 proved that, contrary to the opinion of earlier observers, 

 the seat of sensitiveness is not at the root of the jet where 

 it leaves the orifice, but at the place of resolution into 

 drops. As in Sir W. Thomson's water-dropping ap- 

 paratus for atmospheric electricity, the drops carry away 

 with them an electric charge, which may be collected by 

 receiving the water in an insulated vessel. 



I have lately succeeded in proving that the normal 

 scattering of a nearly vertical jet is due to the rebomid of 

 the drops when they come into collision with one another. 

 Such collisions are inevitable in consequence of the diffe- 

 rent velocities acquired by the drops under the action of 

 the capillary force, as they break away irregularly from 

 the continuous portion of the jet. Even when the reso- 

 lution is regularised by the action of external vibrations 

 of suitable frequency, as in the beautiful experiments of 

 Savart and Plateau, the drops must still come into contact 

 before they reach the summit of their parabolic path. In 

 the case of a continuous jet the "equation of continuity" 

 shows that as the jet loses velocity in ascending, it must 

 increase in section. When the stream consists of drops 

 following the same path in single file, no such increase of 

 section is possible, and then the constancy of the total 

 stream requires a gradual approximation of the drops, 

 which in the case of a nearly vertical direction of motion 

 cannot stop short of actual contact. Regular vibration 

 has, however, the effect of postponing the collisions and 

 consequent scattering of the drops, and in the case of a 

 direction of motion less nearly vertical may prevent them 

 altogether. 



Under moderate electrical influence there is no material 

 change in the resolution into drops, nor in the subse- 

 quent motion of the drops up to the moment of collision. 

 The difference begins here. Instead of rebounding after 

 collision, as the unelectrified drops of clean water gene- 

 rally or always do, the electrified drops coalesce, and thus 

 the jet is no longer scattered about. W^hen the electrical 

 influence is more powerful, the repulsion between the 

 drops is sufficient to prevent actual contact, and then of 

 course there is no opportunity for amalgamation, 



' "'The Influence of Electricity en Colliding Water Drops." Paper read 

 at the Royal Society by Lord Rayleigh, F.R.S. 



