Astronomical and Nautical Collections. , 316 
tiyely ; the former expressing the acceleration of the inverted semidiurnal 
tide, and the latter the retardation of the direct diurnal tide, by the effect of 
friction, the sum of the former and twice the latter is 39° 53’, or very nearly a 
right angle ; so that the interval, thus computed, instead of one tenth of a day 
should be a little more than an eighth, It would, however, be necessary to com- 
pare the height of the water at different intervals before and after high water, 
in order to obtain the progressive magnitude of the diurnal tide with sufficient 
accuracy to allow us to place any reliance on the result of this computation. 
With respect to the disappearance of the diurnal tide in an ocean of equa- 
ble depth, no doubt the depth must be equable in order that it may disappear, 
but it must alse be evanescent. In fact, it is not conceivable in what other man- 
ner the equability of depth can possibly produce such an effect ; for there is no 
natural nor assignable relation between the period of revolution and that of 
diurnal tide; the effects are just the same as if the earth were at rest, and the 
attracting body moved round in a day, or in two days ; and it is impossible to 
admit the accuracy of any refined method of investigation, from which Mr. 
Laplace has obtained a result so clearly contradictory to the first principles of 
mechanics. 
ii. An easy Method of comparing the Time indicated by any Num- 
ber of CHRonoMETERS with the given Time at a certain Station. 
By the Rey, Fearon Fauttows, M.A., F.R.S., Astronomer at 
the Cape of Good Hope. 
Ler a transit instrument, or even a sextant with an artificial ho- 
rizon, be established in a conspicuous situation on shore, where a 
clock can always be regulated to true time: then provide a power- 
ful Argand’s lamp with a shutter, so as to be able to darken the 
lamp instantaneously; a few minutes before a certain hour in the 
evening, notice being previously given to the ships, let the lamp be 
lighted, and at the proper instant of time let it be darkened : this 
may be repeated several times at short known intervals. Then the 
errors of every chronometer on board of all the ships, from which 
the lamp can be seen, are immediately found. After a certain 
number of days, let the same be repeated, when the daily ship 
rates will be given, since they are only the differences of these 
errors divided by the number of-days elapsed between the two sets 
of observations. It is evident that for greater truth these observa- 
tions may be repeated at pleasure, No objection can be made from 
