[From this table it appears that D is supposed to contain 36 "inc. el." Now, by Art. 655, D contains 26-3 "globular inches," which is equal to 41 "circular inches," or 36.7 "square inches".] [Specimen of Measurements of thickness by dividing engine.] 590] 2nd rosin plate, [Art. 371, 500] mean diameter 5.6. 591] M. 32. Measures of thickness of crown glass [Arts. 370, 500] measured in the middle of each 16th square part, the numbers being placed in the same situation as the squares. H ⚫062 4.35) I ⚫066 4.36 K 063 4.34 L ⚫068 4:37) M 055 8.68 First got. Made into trial plates and cased in cem[ent] of a greenish colour inclining to blue with a great want of transparency. not used. coated, comp. pow. = 46. Same sort of glass as A and B, but from their greater length and breadth I could not so well judge of their colour. Made up into trial plates. Same kind as C and D. Remains not approp. It is marked on side with single scratch of file, I with 2, and so on to L. Made into trial plates and broke except L. More transparent than the thick plates. not used. The thickness was measured in the middle of each side, beginning with that side to right of letter, the letter being held towards eye. Diam. coating. Comp. power. 2 thickish plates of 8 inc. made into trial plates for 2nd sort, called S and L. Another cut into 4 pieces for trying effect of different varnishes. 2 thin ones of bluish glass coated in order to serve for trial plates to largest plate, and called L and S, but not used. 2 thick plates and 1 thin one rough. 2 white glass plates from Nairne. 4 pieces out of same piece with different sorts of surface. A large piece of whitish plate glass divided into 3 pieces, one used for sliding trial plate. 4 irregular shaped pieces called N, O, P, Q. [Art. 459.] 2 thinnish pieces 5 inches square with very thin plate rosin between. M. 2. 1 piece of much the same kind fastened to piece of crown glass with cement between, used for sliding plate. * [Here follows another series of measures on loose leaves of different sizes.] [The weights in 1st & 2nd column are in ounces, pennyweights and grains (Troy), in the 3rd and 4th in decimals of an ounce, and the 5th is the specific gravity. The number 9-84973 is the logarithm of the number of cubic inches in an ounce of glass.] M. 4. [Gives 1st the length of each side of each piece of glass, and the distance between the middles of opposite sides to hundredths of an inch. 2nd the thickness at each corner and middle of each side to thousandths of an inch. 3rd specific gravity and mean thickness deduced from it for plates A to M of Nairne. [The thicknesses given in Art. 324 are those calculated from the weight in and out of water and the measurement of the sides. They are greater than the measured thicknesses in every case. e.] 594] M. 6. Measures of thickness & of green glass cylinder. Longest cylinder: a mark made with file near middle. The 1st column is the distance in inches of the point to which cylinder is immersed in water from the scratch. The 2nd column is weight required to balance it in that position. The 3rd is the same thing in the 2nd trial. The 4th is the difference of these numbers, or bulk of intermediate portion of glass. The 5th is the same thing in 2nd trial, and The 6th is the mean between them. The 7th is the circumference in the middle of that space. [after this a table for the narrower half of 1st cylinder, and in M. 7 for 2nd, 3rd and 4th cylinders. M. 8 and M. 9 is a table of 11 columns. M. 10. Measures of the circumference and substance of glass in jars and cylinder. Marks with file are made at the extremities of the whole space, and the numbers begin with the space marked with double mark. By mean circumference is meant the mean between the inside and outside circumference. The circumference was measured by a slip of tinfoil put round, and the intersection marked with knife. The substance of glass was found by hanging it to end of sliding ruler fastened to one end of balance, and weighing it in water; and by sliding the ruler I made more or less of it to be immersed, and knew the difference of the space immersed. M. 11. Specific gravity of different pieces of white glass. The small jar being broke, a 2nd was measured. Thickness measured by calipers in 4 different rows parallel to axis and in 5 different places in each row, beginning at a scratch with a file near bottom. [Here follow the measures.] The thickness was then tried in 4 different parts of circumference at 4.4 inc. distance from scratch. It was then weighed in water in the same manner as the others. The jar was dried before each trial, and before the 3rd was rubbed with solut. p. ash*, which made the water stick less to side, for which reason it is supposed most exact. The circumference was measured in two parts of the middle space, and they came out both the same. 595] M. 12. Measures of coatings to jars and cylind.† A coating made to 2nd small jar extending to 4.4 inches from scratch. Comp. power 680·7. Coating to white cylinder extends 9.86 inches from double mark. Comp. power 684.1. A coating made to 4th green cyl. extending 7 inches from mark. Comp. power 318-2. A mark was made on wide part, extending 7·16 inc. from new mark. Comp. power 600-7. M. 13. A mark made on 2nd green cylinder 11 inches from first towards thick end, and the tube cut off about 1 inch from 1st mark. A coating made to the thick part extending 8.55 inches from 2nd mark. Comp. power 600. [Pearl ash.] = + [See Art. 383. The computed power here is 8 times the true value, and there is no correction for spreading of electricity.] |