202 Instructions for the Scientific Expedition 



of an astronomical nature by which the time can be ascertained 

 within a minute or two. 



The Council now propose to extend these observations in regular 

 series to the 21st of every month, with the same reservation with 

 regard to Sundays. 



It is to be hoped that in regular meteorological observations the 

 six-hourly observations may not be found to be impracticable through- 

 out the year ; but in any case where it may be impossible to observe 

 regularly at 3 a.m., an effort should be made to include the hour on 

 the days of the new and full moon, and quadratures, or at least on 

 the days of the new and full moon ; — as it must be borne in mind, 

 that in what concerns the great meteorological questions on which 

 the most interesting features of the subject depend, the night is quite 

 as important as the day, and has been hitherto far too much neglected. 



Whatever hours, however, may be selected for the regular series 

 of observations, the greatest care should be taken not to substitute 

 or interpolate in an irregular manner observations at any other hours. 



It is much to be wished that occasional observations may be made 

 under remarkable circumstances, such as during great rises or great 

 falls of the barometer, at the period of great storms, earthquakes, 

 &c. ; but such observations should be registered apart. 



The barometer should be placed in an apartment subject to as 

 little variation of temperature as possible, and in a good light ; and 

 to facilitate night observations, an arrangement should be made for 

 placing behind it a light screened by a sheet of white paper, or other 

 diaphanous substance. Great care should be taken to fix it in a 

 perpendicular position by the plumb-line. Its height must be care- 

 fully ascertained above some permanent and easily-recoverable mark, 

 either in the building in which it is situated, or in some more per- 

 manent building, or rock, in its immediate vicinity ; and no pains 

 should be spared to ascertain the relation which such mark may bear 

 to the level of high and of low water at spring tides, and ultimately 

 to the mean level of the sea. 



Changes in the adjustments of meteorological instruments should 

 be most carefully avoided ; but whenever any alteration may be ab- 

 solutely necessary, they should be made with all deliberation, scru- 

 pulously noticed in the register, and the exact amount of the change 

 thence arising in the reading of the instrument under re-adjustment 

 ascertained. As far as possible, registers of meteorological observa- 

 tions should be complete ; but if, by unavoidable circumstances of 

 absence, or from other causes, blanks occur, no attempts to fill them 

 up by general recollection, or by the apparent course of the numbers 

 before and after, should ever be made. 



The observatories established by the Government are furnished 

 with two barometers each, of Newman's construction — the one a 

 standard, and the other portable ; and they are accompanied by ac- 

 curate directions for fixing and observing them. 



The standard instrument is of large dimensions, its tube being 

 of the diameter of 0*6 inch. It requires two adjustments: 1st, The 

 whole scale, which is of brass, is moveable, and terminates in an 



