the morphological representative of the mid gut, and that the liver really arises as a diverticulum from it.

Four varieties of embryos, taken from animals answering the description of C. astroides, are described; but as it was found impossible to make out any differences in the adults, the question whether these varieties represent distinct species or polymorphic forms is left undecided.

II. "On the Determination of the Constants of the Cup Anemometer by Experiments with a Whirling Machine." By the Rev. T. R. ROBINSON, D.D., F.R.S., &c. Received March 14, 1878.

(Abstract.)

In his description of the cup anemometer (Transactions Royal Irish Academy, Vol. XXII), Dr. Robinson inferred from experiments on a very limited scale with Robins' whirling machine, that the ultimate ratio of the wind's velocity to that of the centre of the cups =3. Some recent experiments by M. Dohrandt show that this number is too great; but as some of the details appeared objectionable, and as they did not include all the necessary data for determining the constants, the author was desirous of repeating them. He was enabled to do this by a liberal grant from the Royal Society, and the results are given in this paper.

After describing the apparatus and the locality in which it was established, he proceeds to explain the conditions of an anemometer's action. Considering only two opposite cups, and supposing them in motion, the pressure on the concave surface is as that surface and the square of the resultant of the wind's velocity V and v, that of the anemometer, and as a, the pressure of an unit V on the cup normal to the arm.

This is opposed, 1. By the pressure of a similar resultant on the convex surfaces, and ά, another coefficient, also normal to the arm, but quite different from a; 2. By various resistances depending on v2; and 3. By the friction of the machine estimated at the centres of the

cups.

a and á are functions of V, v, and 0, the angle which the wind makes with the arm, but it is impossible to determine them à priori in the present state of hydrodynamics. It is, however, obvious that if V be constant, the mean values of v, a, and á through one revolution will soon also become constant, and as the mean impelling and resisting forces balance each other, the condition of permanent motion is expressed by an equation of the form aV2-2ßVv – yv2—F=0; or V2-2xVv-yv2=0 (1), which, if the constants are known, gives

F

a

V in terms of v and F. Conversely, if we have a sufficient number of values of V, v, and F, we can determine a, ß, and 7.

Unfortunately, there is much difficulty in obtaining some of these values. We cannot produce wind of known velocity, and must substitute for it the translation of the anemometer through the air with a known speed.*

The most convenient mode of doing this which occurred to him was the attaching the anemometer to a whirling machine. In this case, however, the rotation of the apparatus causes an air-vortex, whose motion must be subtracted from that of the arm to give what is assumed as the effective V. The means by which this vortex current was measured are described; they show that it is exceedingly irregular, and that it is accompanied by a radial current still more disorderly. We get v with sufficient accuracy, but it is otherwise with F. Of this there are four kinds acting in these experiments. 1. That due to the weight of the moving parts of the anemometer; 2. That caused by the action of a brake, intended to diminish v in respect of V; 3. That produced by the lateral pressure of its axle on its supports, produced by the wind, &c.; and, 4. That due to the centrifugal force arising from the circular track of the anemometer's centre, which in the actual arrangement pressed the axle outwards. The modes of measuring these are described; but this part of the work proved far from satisfactory. The ground where the apparatus was established was affected by tremors from the action of machinery, which made all these frictions variable; and as he had the use of it for a very limited time, it was impossible to repeat the work with the precautions taught by experience.

The constant a was determined by connecting a strong clock-spring with an arm of the anemometer and that of the whirling machine. When the whirl was rotated the anemometer tended the spring till its elastic force equalled the air's pressure on the cups. Then a brakefriction was applied much beyond the power of the spring, which kept the anemometer in its place; V was determined, and the tension T-F given by a graduated circle fixed on the axle. Then a= V2

These measures showed that equation (I) contained no notable term

In 1845 it occurred to Dr. Robinson to carry an anemometer on a railway, for which full opportunity was offered by a valued friend, Mr. Bergin, then Secretary of the Dublin and Kingstown Railway. He gave it up after carefully considering the disturbing influences and the precautions that were required. The space to be traversed should have no curves; should be perfectly unenclosed; should not be very long; and at each end of it an anemometer should be established to keep record of any wind. The experimental instrument should be 20 or 30 feet before the engine, so as to be clear of the air which it drives before it, and should be carried by a platform so formed as to present little resistance, and 10 or 12 feet above it.

of V except the square; secondly, that with cups of a given size a is not changed by varying the arms from 24 to 12; and, thirdly, that it is as the area of the cups.

Five instruments were used. No. I, cups 9 inches, arms 24, like the Kew ones; No. II, cups 4 inches, arms 24; No. III, cups 9 inches, arms 12; No. IV, cups 4 inches, arms 12; No. V, cups semi-cylinders, 9 inches by 9. The results with these are given in tables which show along with V, v, and W the vortex current, the frictions 1, 2, and 4, the air's V density, and =m. This last is seen to differ in each anemometer, and

v

to be variable in each, ranging from 21:58 to 2:32. It increases with F and decreases as v increases in such a manner as shows that it will remain finite even when v is quasi-infinite.

and treating those for each instrument by minimum squares, he got values for a, ẞ, and y, which, however, were unsatisfactory.

Dividing the 40 belonging to No. III into three groups, in the first of which are all whose v<5, in the second those from 5 to 9, in the third those >9, each gave discordant values for the constants. Those of a least so, those of y most; the latter, indeed, rambled so much that no reliance could be placed on them. The matter was not mended by combining the entire. Thinking this discordancy might arise from equ. (I) containing a term dv, he tried this, but with a result so much worse that such a term, if it exist, can have no sensible influence. The results for the other instruments were similar. In fact, the method of minimum squares applies very imperfectly to a case like this, where the coefficients of the unknown quantities and the absolute terms are themselves affected with errors. Besides this, in the final equations of this process the coefficients of y and ẞ are so much less than those of a that they, especially 7, must be less accurately determined. It is also to be noted that these constants may be changed within certain limits, and still satisfy the equations approximately.

It was, however, suggested to him by Professor Stokes that, as equ. (II) has only two variables, 7 and §, it could be plotted on a plane surface, and this gave valuable information. The plottings for the five instruments are given, and show distinctly both the general agreement of (I) with the observations and the cause of the discordances.

Though in all the dots are much scattered, yet through a large portion of each the general direction is a right line with (in some cases) a barely perceptible downward curvature.

Since the curvature is nearly as y this last must be very small, and assuming it=0, the equation aV2-2ẞVv-F-0 will be sufficiently accurate. Towards the vertex of the curves (where v is small) the

dots are so straggling that nothing can be made of them. In No. II, and still more in No. IV, they show that the frictions were considerably astray. Guided by these indications, and assuming for a nine-tenths of his measures of that constant, he deduced for Nos. I and III values of ẞ and y so nearly equal as to make it probable that their means would satisfy both. This would give x=11282; x2+y=z=1340.

F

The positive root of (I) gives V=v{2+√2+}. (III).

Computing from this, we find AV-obs. - calc., of which tables are given for the five anemometers. As might be expected from the plottings, they are not very close, but show no systematic deviation from the law denoted by (I). So it may be assumed exact for all practical purposes through a range of V from 5 to 42 miles, and of F from 113 to 3277 grains. For No. III the probable error=±0·45. In both the errors are less on the hypothesis y=0. In No. II these mean constants fail, but others deduced for it represent the series, though not so well as in the preceding; here also y=0 is not inferior. In No. IV the frictions seem to have been deranged so much that the entire series cannot be well represented by any constants. Circumstances detailed in the paper account for this. No. V, cylinder cups, is the best of all. If, as seems probable, a and z are the same for all hemispherical anemometers, the difference between their indications will depend solely on, and using the values given above, the limiting

F

a

value of m=2.286, instead of 3. Though if these experiments were repeated with Dr. Robinson's present experience, and in an undisturbed locality, better results might be obtained, yet the errors of the vortex current would still cause uncertainty; and he intends to try another plan.

The anemometer No. I, with its apparatus duly altered, is now erected on the roof of the dwelling-house 22 feet from the Kew one also there, to which it is exactly similar. Denoting the latter as S (the standard one), the other, E, is to be loaded with a brake friction, which will make its v less than that of S; when this has gone on long enough to ensure that an equal amount of wind has passed each instrument, a larger brake friction is applied to E. We shall thus have three equations (1), but four unknown quantities, a, a, V, y. a, however, is certainly known nearly by the measures already made. F also can now be measured with far greater precision. The chief difficulty to be feared is the unsteadiness of the wind during each experiment; but as the time of each revolution of the two anemometers is recorded on the chronograph, it will be possible to eliminate this element of doubt by selecting those times which have a given ratio.

III. "On the Action of Ozone on Nuclei." By CHARLES TOMLINSON, F.R.S. Received March 14, 1878.

After the reading of my paper on the 21st ultimo, Professor Stokes was so good as to suggest that some of my experiments should be repeated with ozone, prepared by the action of a coil, instead of that of phosphorus.

Professor Guthrie was so kind as to furnish me with a couple of bottles of ozone, prepared by sending oxygen slowly through Wills's generator in connexion with an induction coil.

The ozone was used soon after it was prepared, and in the following

manner :

Oil of cajuput was distilled, and the fresh distillate was found to be inactive on a supersaturated solution of sodic sulphate (3 to 1), although it was repeatedly shaken up with the solution. The newlydistilled oil was poured into one of the bottles of ozone, and shaken up with it, and then left for about fifteen minutes. It was dropped into nine flasks of the solution just named, and was active in all. In some of the flasks the solution became solid as soon as the ozonised oil reached the surface; in others, immediately on shaking the flask, or after a short interval of repose; while, in a third set, after adding the oil, the axis of the flask being brought into a nearly horizontal position, the flask was made to revolve slowly, when the solution solidified against the side, so as to form a kind of lining to it.

On the 12th March the wind was N.E., and the ozone in the air was very active on test paper. A paraffin oil of high boiling point was distilled, and specimens of the fresh distillate were powerfully active on a solution of sodic sulphate (2 to 1). A similar oil distilled during a S. or W. wind, as noticed in a former note, was inactive.

To a solution of sodic sulphate (3 to 1), containing oil of cajuput in an inactive condition, a solution of hydric peroxide was added, but it had no effect in rendering the oil active. The flask was shaken every day during a week, and the only effect was to liberate bubbles of gas. On adding to this flask a drop or two of the ozonised oil, the solution immediately became solid.

(23rd March.) The inactive distillates of cajuput and paraffin oils, shaken up several times during about half-an-hour with pure oxygen gas, became active. Test papers, suspended in the bottles, showed the presence of ozone. Washed castor oil, similarly treated, remained inactive; but shaken up with ozone, and left in contact with it for some hours, became active.

I repeated the experiment, described in a former note, on the activity of charcoal, on which Pellogio founds his theory of absorption. Pieces of box-wood, buried in sand, were heated in a crucible during