In referring to the works of Mr. Cuthbertson and Mr. Singer, my object has been solely to elucidate an intricate, but interesting, philosophical inquiry; and I hope it will be understood that in so doing, it is my wish to preserve every proper respect for the exertions of two able and ingenious men, whose loss the scientific world has so much to regret.

45. I shall now conclude with a short recapitulation of a few facts, which seem to be established by the preceding inquiries:

1-An electrical accumulation may be supposed to proceed by equal increments.

A coated surface charging in any degree short of saturation, receives equal quantities in equal times, all other things remaining the same

The quantity passing from the outer coating, is always proportional to the quantity added to the inner.

2-The quantity of matter accumulated, may be estimated by the revolutions of the plate of the electrical machine, supposing it in a state of uniform excitation; or it may be measured by the explosions of a jar connected with the outer coatings.

It is as the surface multiplied by the interval which the accumulation can pass:

When the surface is constant it is as the interval:

When the interval is constant it is as the surface.

It is also as the surface multiplied by the square root of the free action.

When the surface is constant, it is therefore as the square root of the attractive force.

3-The interval which the accumulation can pass, is directly proportional to the quantity of matter, and inversely proportional to the surface:

It is as the quantity divided by the surface:

If the matter and surface be either increased or decreased in the same proportion, the interval remains the same:

If as the matter be increased, the surface be decreased, the interval will be as the square of the quantity of matter.

4-The force of electrical attraction varies in the inverse ratio of the square of the distance between the points of contact of the opposed conductors, supposing the surfaces to be plane and parallel; or otherwise between two points, which fall within the respective hemispheres, at a distance equal to one-fifth of the radius, supposing the opposed surfaces to be spherical.

5 The free action is in a direct proportion to the square of the quantity of matter, and in an inverse proportion to the square of the surface.

It is directly as the effect of the explosion on a metallic wire, all other things remaining the same.

If the matter and the surface increase or decrease together, and in the same proportion, the attractive force remains the

same.

If as the matter be increased, the surface be decreased, the attractive force is as the fourth power of the quantity of

matter.

6-The effect of an electrical explosion, on a metallic wire, depends exclusively on the quantity of matter, and is not influenced by the intensity or free action.

It is diminished by accumulating the matter on a divided surface.

It is as the square of the quantity of the matter.

It is as the square of the interval which the accumulation can pass.

It is directly as the attractive force of the free action, all other things remaining, in each case, the same.

It is as the momentum with which the explosion pervades the metal.

Plymouth, November 17, 1825.

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III.

PARTICULARS OF THE CONSTRUCTION OF A CAST-IRON BRIDGE OVER THE LARY NEAR PLYMOUTH, BY JAMES M. RENDEL, CIVIL ENGINEER; MEMBER OF THE ROYAL INSTITUTION OF CIVIL ENGINEERS; AND OF THE PLYMOUTH INSTITUTION.

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THE Construction of bridges of large dimensions has, every civilized age and country, been considered an object of general interest. Nor is this to be wondered at, when we regard their utility, or the difficulties to be encountered in their erection. It is not however my intention to attempt the history of this interesting species of architecture-It has already been amply discussed in several valuable treatises-All that I propose in this paper, is to describe a work of great local importance, of difficult construction, and, in some respects, of novel arrangement.

The Lary bridge is constructed over an estuary, from which it derives its name, and is distant from Plymouth about one mile and a quarter.

It connects a large agricultural district, on the southern shores of the county, with the populous and improving neighbourhood of Plymouth.