Experiment with the wal

nut.

detached from the old trees, and employed as grafts, would still retain the character and habits of bearing branches.

Having therefore planted in the spring of 1799 some walnut trees, of two years old, in garden pots, I raised them up to the bearing branches of an old walnut tree, by placing them on the top of poles placed in the earth; and I grafted them, by approach, with parts of the bearing branches of the old tree. A union took place during the summer, and in the autumn the grafts were detached from the parent stock. The plants thus obtained were planted in a nursery, and, without any peculiar care or management, produced both male and female blossoms in the third succeeding spring, and have since afforded blossoms every season. The frost has, however, rendered their blossoms, as well as those of other trees in their vicinity, wholly unproductive during the last three years, and in the spring of 1805, almost wholly With the mul. destroyed the wood of the preceding year. A similar expeberry. riment was made in the same year, but under many disadvantages, on the mulberry tree. I had not any young plants of this tree, and therefore could only make the experiment with scions of one year old; and of these I had only two, which had sprung from the roots of a young tree, in the preceding year. These were planted in pots, and raised to the bearing branches of an old tree, in the manner I have already described in speaking of the walnut tree. One of these scions died; the other, which had but very few roots, succeeded; and the young grafted tree bore fruit the third year, and has continued annually productive. In the last spring I introduced it into my vinery, where its fruit ripened, in the greatest state of perfection, in the beginning of the present month, [January, 1807].

Grafting by ap proach best for them.

Both the walnut and mulberry tree succeed so ill when grafted, unless by approach, that I can scarcely recommend attempts to propagate them in any other way; but when they succeed by other modes of grafting, nearly the same advantages will probably be obtained: the habit of the bearing branch is, however, least disturbed by grafting by approach.

Spanish ches- The Spanish chesnut succeeds readily when grafted in nut succeeds almost any of the usual ways, and when the grafts are taken

any way.

from

coloured concentric Rings.

h

a

from bearing branches, the young trees afford blossoms in the succeeding year: and I am much inclined to think, from experiments I have made on this tree, that by selecting those varieties which ripen their fruit early in the autumn, and by propagating with grafts or buds from young and vigorous trees of that kind, which have just attained the age necessary to enable them to bear fruit, it might be cultivated with much advantage in this country, both for its fruit and timber.

Valuable both for its fruit and

timber.

and thus their

I have tried similar experiments on many other species of Tried on many trees, and always with the same result; and I entertain no other trees, doubt, that the effects of time might be thus anticipated in maturity antithe culture of any fruit, which is not produced till the seed- cipated, ling trees acquire a considerable age. For I am thoroughly confident, from very extensive and long experience, that the graft derives nutriment only, and not growth, from the young stock in which it is inserted; and that with the life of the parent stock the graft retains its habits and its constitution.

V.

Experiments for investigating the Cause of the coloured concentric Rings, discovered by Sir ISAAC NEWTON, between two Object-glasses laid upon one another. By WILLIAM HERSCHEL, L. L. D. F. R.S.

(Concluded from p. 142.)

XIX. Of the Place where the different Sets of Rings are to be seen.

By an application of the same course of the rays, we may place where

are seen.

now also determine the situation of the place, where the dif- the different sets of rings ferent sets of rings are seen: for, according to what has been said in the foregoing article, the situation of the primary set should be between the lens and the surface of the lookingglass and the place of the secondary one at the metalline roating of the lowest surface. To try whether this be actually as represented, let us substitute a metalline mirror VOL. XIX.-MARCH, 1908. with

N

Eye-glass re

quires a differ

ent adjustment for each set.

Connexion between different gets.

with a slip of glass laid upon it in the room of the piece of looking-glass; and let there be interposed a short bit of wood, one tenth of an inch thick, between the slip of glass and the mirror, so as to keep up that end of the slip which is towards the light. This arrangement is represented in Pl.V, fig. 9, where both sets of rays are delineated. Then if we interpose a narrow tapering strip of card, discoloured with japan ink, between the slip of glass and the mirror, so as to cover it at 7, we do not only still perceive the primary set, but see it better than before: which proves, that, being situated above the slip of glass, the card below cannot cover it. If on the contrary we insert the strip of card far enough, that it may at the same time cover the mirror both at 4 and at 7, we shall lose the secondary set, which proves, that its situation was on the face of the mirror.

When several sets of rings are to be perceived by the same eye-glass, and they are placed at different distances, a particular adjustment of it will be required for each set, in order to see it well defined. This will be very sensible when we attempt to see three or four sets, each of them situated lower than the preceding; for without a previous adjustment to the distance of the set intended to be viewed, we shall be seldom successful; and this is therefore a corroborating proof of the situation, that has been assigned to different sets of rings.

XX. Of the Connection between different Sets of Rings.

It will now be easy to explain in what manner different sets of rings are connected, and why they have been called primary and dependent. When the incident rays come to the point of contact, and form a set of rings, I call it the primary one: when this is formed, some of the rays are continued by transmission or reflection, but modified so as to convey an image of the primary set with opposite colours forward through any number of successive transmissions or reflections; whenever this image comes to the eye, a set of rings will again be seen, which is a dependent one, Many proofs of the dependency of the second, third, and fourth sets of rings upon their primary one may be given; I shall only mention a few.

Proofs that all, When two sets of rings are seen by a lens placed upon a

looking