The description and use of a joynt-rule fitted with lines for the finding the hour of the day and azimuth of the sun, to any particular latitude, or, to apply the same generally to any latitude : together with all the uses of Gunters quadrant applyed thereunto ... / contriv'd & written by J. Brown, philomath.

CHAP II.

The Uses of the Rule follow.

1. To Rectifie or set the Rule to his true Angle.

OPen the Rule to 60 degrees, which is done thus, (indifferent∣ly:) make the lines on the head, and the lines on the other leg, meet in a streight line; then is the Scale of Al∣titudes and the line of Hours set to an Angle of 60 degrees, the rectifying point, being the center of that Angle; Or to do it more exactly, do thus: put one point of a pair of Compasses into the rectifying point, then open the other to 10, 20, 30, or 40, on the Scale of Altitudes, the Compasses so opened, and the point yet remaining in the re∣ctifying point, turn the other to that margenal line in the line of hours, that cuts the rectifying point, and there stay it; then remove the point that was fix∣ed

in the rectifying point, and open or shut the Rule, till the point of the Compasses will touch 10, 20, 30, or 40, being the point you set the Com∣passes too in the Scale of Altitudes, in the innermost line that cuts the center, and the rectifying point, then is it set exactly to 60 degrees, and fitted for observation.

2. To finde the Suns Altitude at any time.

Put a pin in the center hole, at the upper end of the Scale of Altitudes, and on the pin hang a thread and plum∣met; then if the Sun be low, that is to say, under 25 degrees high, as in the winter it will always be, then lift up the moveable leg, where the moneths and the degrees be, till the shadow of the end fall just on the meeting of that leg with the head, then the thread shall shew the Suns altitude, counting from 60|0 towards the head, either 10, 20, 25, or any degree between.

But if the Sun be above 25 or 30 de∣grees

high, lift up the head leg till the shadow of that play as before, or make the shadow of the pin in the center hole play on the innermost line of the Scale of Altitudes where the pin stand∣eth, then the thread will fall on the degree, and part of a degree that his true altitude shall be.

But if the Sun be in a cloud, and can not be seen so as to give a shadow, then look up along by the head-leg, or move∣able leg, just against the middle of the round body of the Sun, and the thread playing evenly by the degrees, shall show the true altitude required. The like must you do for a Star, or any other object, whose altitude you would find.

3. Having found the Suns altitude, and the day of the moneth, to finde the hour of the day.

Whatsoever you finde the altitude to be, take the same off from the Line of Altitudes, from the center downwards with a pair of Compasses, then lay the thread (being put over the pin) on the

day of the moneth, then put one foot of the Compasses in the line of hours, in that line that cuts the rectifying point, and carry it further off, or nigher, till the other foot of the Compass being turned about, will just touch the thred, at the nearest distance, then the point of the Compasses on the line of hours, shall shew the true hour and minute of the day required.

Example on the 2. of July.

1. I observe the altitude in the mor∣ning, and I finde it to be 30 degrees high, then laying the thread on the day of the moneth, and taking 30 degrees from the Scale of Altitudes, and put∣ting one point in the line of hours, till the other point turned about, will but just touch the th••ead, and I finde it to 23 minutes past 7, but if it had been in the afternoon, it would have been 37 minutes past 4.

2. Again, on the tenth of August in the Afternoon, at 20 degrees high, I take 20 degrees from the Scale of Al∣tudes,

and laying the thread on the day of the moneth, viz. the tenth aforesaid, counting from the name at the begin∣ning of August, toward September, and carrying the Compasses in the line of hours, till the other point doth but just touch the thread, and you shall finde it to be 54 minutes past 4 a clock.

3. Again, on the 11. of December at 15 degrees high, work as before, and you shall finde it to be just 12 a clock; but to work this, you must lay the Rule down on something, and extend the thread beyond the Rule, for the nighest distance will happen on the out-side of the Rule.

4. Again, on the 11 of Iune at noon I finde the altitude to be 62 degrees high, then laying the thread on the 10th or 11th of Iune, for then a day is un∣sensible, and working as before, you shal finde the point of the Compasses to stay at just 12 a clock, the time required for that altitude.

4. To finde the Suns rising any day in the year.

Lay the thread on the day of the month, and in the line of hours it sheweth the true hour and minute of the Suns rising or setting; for the rising, count the morning hours; and for the setting, count the evening hours.

5. To finde if any place lye level, or nor.

Open the rule to his true angle of 60 degrees, then set the moveable leg upon the place you would make level, and if the thread play just on 60 degrees, it is a true level place, or else not.

6. To try if any thing be upright or not.

Hang a thread and plummet on the center, then aply the head leg of the rule to the wall or post, and if it be up∣right, the thread will play just on the innermost line of the scale of altitudes, or else not.