RIR. G. H. MAKINS ON 111.-On an Improved Assay Balance. BY GEORGEH. MAKINS. Having occasion some little time since for an assay balance and being well aware of the points wherein those in use here are deficient I applied myself to the task of so arranging existing materials as to produce if I could a more effective instrument. Two forms of assay balances are most common in England. The first is very little more than an exceedingly delicate pair of ordinary scales; in fact a very light scale-maker‘s beam adjusted as they are accustomed to do by carefully ‘‘setting” it so as to obtain correct length of arm and straight line of fulcrum and points of suspension. The second is an instrument imported from France or better made here upon the French plan.Of these tbc French are but an improvement upon thc first class; the hcams (of almost all) being permanently adjusted whcii finished. Thosc however> ma& by AN IMPROVED ASSAY BALANCE. Mr. Oertling upon this plan are furnished with the requisite adjust- ments and are very superior in point of detail and workmanship. But the beams of all contain too much metal and that especially in parts where its presence interferes with their action by imparting a certain amount of inertia. And lastly their stands and move-ments are very far from convenient. The essentials in an assay balance appear to be these first that it should be constant so that certain differences of value in weights should always produce the same difference of indication ; secondly it should be exceedingly quick in indicating; and thirdly very sen- sible and consequently well affected by slight differences.These two last requirements are sonicwhat incompatible for in proportion as you increase quickness of action you must diminish sensibility by lowering the centre of gravity of the system ;and it is in the union of these two necessary qualifications that the value of the balance now before the Society lies. The beam of this balance is what is called a skeleton-beam 10 inches long an inch deep at the fulcrum tapering off to 5 at each end. It is about -&of an inch thick in the centre decreasing in the same way to of an inch. As little metal as possible is left in it; thus in the centre there is but just enough to allow of secure fixing for the knife-edge; and at the ends for the adjustments for length of arm &c.The latter are effected very much in the same way as in Robinson’s balance in which an oblique saw-cut is made nearly through the metal at the ends of the beam which cut is capable of being opened or closed by pressing-screws In the present case a loose piece is put on and made similarly adjustable by screws. Thus we obtain the adjustment for length of arm. The bearings for the pendants are two hard steel points at each end adjustable for the straight line by having a fine screw cut on each and provided with fixing-nuts. By these the points can be screwed vertically up or down through the horizontal plate formed at the end of the beam. The pendants are hung on these points by a small steel plate in the underside of which a cup-shaped cavity is turned for the one and a groove hollowed out from the back towards the front for the other.Had two cups been employed it would have been next to im-possible even by the most careful workmanship to have secured their concentricity with the points. A small steel hook for the pan- chains passes vertically down in a notch in the horizontal plate at the end of the beam. MR. G. H. MAKINS ON This last arrangement is due to Mr. O$rtling whom I employed to make this instrument; for in the drawings I sent to him I had put but a single point at each end being fully persuaded how much quickness and delicacy are ensured by the least possible friction of the pendants.I had provided against their swinging round which was almost sure to take place upon a single point by having the edges of the notches through which they were to pass worked to a kind of knife-edge on each side. Mr. Oertling how- ever thought that two would be necessary and that the friction in them would be less than even if one were used. The weight of the beam with all its fixed appendages is only 103 grains. Its bearings are of agate worked to elliptical surfaces instead of being as usual plain. Here again but a point of the knife-edge is allowed to bear upon the agate. Bearing in mind the very small weight these balances would have to carry (and I never load mine with more than 25 grains) I had no hesitation in thus reducing all parts of contact where friction during action occurs to the sniallest possible dimensions virtually indeed to points.Nor have these parts been found to fail from blunting by wear as might have been anticipated; at least in the case of one which I have daily in use I know that I havernade more than ten thousand weighings in it and not the least diminution of sensibility is as yet observable. The stand is massive in its construction in order that when rapidly put into action no tremulousness may be communicated to the beam. 1 give here an outline drawing of the instrument (made to a scale) in order to exhibit its solidity in contrast with the delicacy of the beam and its appurtenances. It corisists of two stout pillars of + an inrh diameter and 62 inches long fixed on a base a of an inch thick.Upon the upper end of these is fixed a table which has two upright pieces rising from it to which are cemented the agate bearings. A second corresponding table is attached to the movement rods which pass down the pillars. This table has two mortices in it for the passage of the upright pieces which carry the agates and upon these uprights it slides up and down. On the outside of this second table is a crutch on each side ; these lift off the beam from its bear- ings when throwing it out of action. The movement lever on being depressed first however acts upon the arms of two rollers which are fixed under the lantern and whose opposite arms depress the ivory tables which support the pans ; AN IMPROVED ASSAY BALANCE.this roller motion is partitularly free and pleasant in use. By the time the tables are well away the lever has reached a connecting II I C.H.M. stirrup between the movement rods and begins to drop the beam upon the agates.* In order to have the smallest possible contact between the under side of the pans and the tables the latter have hemispherical eminences turned upon them and the pans themselves have a curve given to them of a radius just equal to the distance between the ivory table and the point of suspension ; whereby should they swing out of the perpendicular during weighing they will nevertheless be caught by the tables when they rise up to them. There are adjustments both for the amount of fall of the fulcrum to the agates and of rise of the ivory tables to the pans; the former is however very small in amount By the pillars being fixed at a distance of 13 inch from each other a good space is obtained for a scale; while by prolonging the index-needle to rather more than 6 inches downwards very open degrees are obtained.And besides this great advantage the motions of the index-needle are brought nearly upon a level with the pans. To those who are used to a descending index (as in all good * The movement and "rider" apparatus are both omitted in the above drawing for t.he sake of greater distinctness. PROFESSOR W0€1I ER 0N chemical balances) the comfort of this arrangement will be at once apparent ;for the eye has not to travel a distance between the pans and ir?dex (as is the case in the balances to which I just now alluded) but the whole are under view at once.Much praise is due to the maker for the very beautiful work-manship he has put into these instruments and that more especially in the beams. Without this perfect degree of execution of the work they would be uncertain in action and possess less capa- bility than a heavier instrument. I haw been encouraged by several members who have had appor-tunities of witnessing its performance to put a brief description of this instrument before the Society in the form of a notice and hope that by so doing I have not been occupying time unprofitably. I should have done so last season but had not one sufficiently long in use to fairly put its powers to the test before the close of the Society’s meetings.