of the Place of Observation. 447 



that had the number of observations been augmented to 

 ten, and a mean of the results taken, a great part of the 

 present error would have been removed. 



I shall conclude these deductions by remarking, that a 

 complete set of observatioos similar to those I have here 

 given may be taken in the space of a quarter of an hour, 

 or twenty minutes, by a single observer, and that they 

 may be facilitated, and rendered a little more accurate, by 

 the assistance of some person to write down the observa- 

 tion at the time : this part of the business, indeed, any one 

 may do, and I am inclined to believe that under such cir- 

 cumstances the greatest error committed, will seldom ex- 

 ceed five miles, but will generally fall short of this distance. 



I have reduced the apparent distance to the true by the 

 method given in the supplement to ihe 3d edition of the 

 requisite Tables, a method both simple and expeditious, and 

 so easy in practice that a child of eleven years of age of 

 moderate capacity might in a short time be fully instructed 

 to perform the calculation. 



I cannot help remarking, that many attempts have been 

 made, and are still making, to construct machines for ihe 

 more easily determining the longitude at sea; and although 

 I am far from wishing to discourage any such attempts 

 when conducted upon scientific principles, yet I am greatly 

 surprised that the means of determining the longitude by 

 the lunar observations should even at this time be thought 

 an operose task. The improvements in the lunar tables, 

 in the construction of sextants, and in the method of re- 

 ducing the apparent to the true distance, have been such as 

 to ensure the observer, with even but a moderate degree of 

 experience, an accuracy far greater than is ever required in 

 nautical practice. It may be said, that the weather is of- 

 tentimes too unfavourable to determine the longitude by 

 the lunar method, and that for several days in the month 

 the moon is invisible, being too near the sun. Here the 

 use of a good time-keeper would be of great advantage, as 

 by it the longitude would be easily carried on between the 

 opportunities which offer, to obtain distances of the sun 

 and moon, or the moon and a star, and even a time-keeper 

 of very moderate performance would answer this purpose 

 with sutficient accuracy for every nautical purpose : would it 

 not therefore be of great advantage to the maritime depart- 

 ment of this country to have youug gentlemen designed 

 for the service of the sea, well educated c/ti shore, both in 

 the praclicf as well as theory of finding tlie longitude by 

 the means here recommended ? 



October 



