(726)
An Extract
SIr, I here present you with a Scheme of the Magnetical Variations, as it was sent me by Capt. Samuel Sturmy, an experienced Seaman, and a Commander of a Merchant Ship for many years; who (as he assures me) took the Observations himself in the presence of Mr. Staynred, an ancient Mathematician, & others, in Rownham-Meadowes by the water-side, in some such approach, I think, to Bristol, as Lime-house or the Fields adjoyning are to London. This (as the Table shews) was taken June 13. 1666; They observed again in the same day of the next year, viz, June 13. 1667; and then they found the Variation increas'd about 6. minutes Westerly.
| Observed June 13. 1668. | |||||||
| Sun's
Observ'd Altitude. |
Magnetical
Azimuth. |
Suns
true Azimuth. |
Variat.
Westerly. | ||||
| Gr. | M. | Gr. | M. | Gr. | M. | Gr. | M. |
| 44 | 20 | 72 | 00 | 70 | 38 | 1 | 22 |
| 39 | 30 | 80 | 00 | 78 | 24 | 1 | 36 |
| 31 | 50 | 90 | 00 | 88 | 26 | 1 | 34 |
| 27 | 40 | 95 | 00 | 93 | 36 | 1 | 24 |
| 23 | 20 | 103 | 00 | 101 | 23 | 1 | 23 |
Now he promiseth to take the Observations in the same Company and Place, on the 13th. June next following, with a Quadrant of 6 foot radius, accurately divided into minutes, and with a very good Needle about 8. inches long; and he doubts not, but the Observations shall be as exactly made, as can be done by any Men in any place of the World.
He adds, that he has found in several places or Meridians, upon his own Observations, from 2. min. to 7. minuts some difference. In this Table he notes the greatest distance or difference to be 14. minutes; and so taking the mean for the true Variation, he concludes it then and there to be just 1. deg, 27. min. viz., June 13, 1666.
The same person promiseth an exact accompt concerning
