450

118040

262 days from July 1, 1871, is March 19, 1872. Ans.

It will be observed that by this method the balance falls due two days earlier than by the method by Double Equation.

Method of Interest.

Rule. Compute the interest at 12% on both sides of the account from the last day of the month preceding the date of the earliest transaction of the account, to the time when each item becomes due. Divide the balance of interest by the interest on the balance of the account for one month. The quotient will be the average term of credit in months, to be reckoned forward from the focal date if the balances of interest and account be on the same side, and backward if these balances be on different sides of the account.

Example. Still employing the same account.

Dr.

Apr.

3, $440, 3 months, Interest 3 months $13.20

66

3 days

6 months

1.32 15.00

66

7 months

28.00

66

10 months

28.00

66

Balance of Interest $53.14

Balance due

$1300.

Balance of Account $450.

Int. on balance 1 month, $4.50.

53.14 months, or 11 mos. 24 days, from March 31, 4.50 1871, which is March 24, 1872-a result differing from both those already given. Yet the three methods are in common use.

The discrepancies arise in great part from calculating interest on a basis of 360 days to the year, but reckoning days exactly as they occur. Thus, by the usual method of reckoning interest, the time from July 1 to Sept. 1, is the same as that from Feb. 1 to Apr. 1, while the time is in the one case 62 days, and in the other 59 days. If the tables on pp. 94 and 95 could be brought into ordinary use, this uncertainty and unfairness could be avoided, while the calculation would be quite as rapid and easy.

Thus, required the interest at 10% on $10,000, from July 1 to Sept. 1, 1870, and from Feb. 1 to March 1, 1871.

Decimal for Sept. 1.66575

By the tables,

July 1=.49589

Difference

.16986

Multiplied by interest of $10,000 for one year, $169.86.

Decimal for Apr. 1=.24658

66

"Feb. 1.08493 Difference .16165

Multiplied by interest of $10,000 for one year, $161.65.

Int. on $10,000, 2 mos., 360 days to year, $166.66.

The amount of stone in a given wall is commonly estimated by the cubic foot, or by the perch.

A perch of masonry is 161 ft. long, 1 ft. deep, and 1 ft. thick, containing 24 cubic ft.

In estimating the amount of stone in a built wall, 23 ft. are allowed for mortar and filling, leaving 22 ft. of stone to the perch of masonry. The usual allowance for mortar to a perch of wall is three pecks of lime and four bushels of sand.

Hence, to find the perches of masonry in α given wall,

Find the contents in cubic ft. and divide by 24.75.

How many perches of stonework in a wall 50 ft. long, 11 ft. high, and 3 ft. thick?

Required the perches of masonry in a wall 491 ft. long, 3 ft. high, 14 ft. thick.

The amount of stone will be

the amount of masonry. Hence, in the examples given, the number of perches of stone in the walls would be 66x=591, and 101×=91, respectively.

BRICKLAYING.

Bricklaying is usually estimated by the thousand bricks.

Bricks are of various dimensions.

Philadelphia or Baltimore front bricks are 81 × 4× 2 in., containing 80.824 cub. in.; North River bricks are 8×3× 2 in., containing 62 cub. in.; Maine bricks are 7× 3 × 2 in., containing 42.082 cub. in.; Milwaukee bricks (light-colored, because there is no iron in the original clay), 81 × 41 × 23 in., containing 83,273 cub. in.; fire bricks, 9×48 × 2 in., containing 100.233 cub. in.

To find the number of bricks in a given wall:To the length and to the thickness of the kind of