6 MR. AIRY ON THE LAWS OF THE TIDES 



f 



It will be seen, in the sequel, that results are obtained relating to the relative 

 levels of the surface of the sea at different places, which if established must be deemed 

 highly important. In order, therefore, to show what confidence is due to the results 

 of relative level, I think it necessary to give, for every instance in which the means 

 of doing so exist, the amount of discrepancy between the results for the difference of 

 level between the same stations when the space between them was traversed by dif- 

 ferent lines. 



Description of marks whose difference of level is ascertained, and courses of the lines of levelling. 



1. 



2. 



3. 



4. 



5. 



6. 



7. 



8. 



9. 

 10. 

 11. 

 12. 

 13. 

 14. 



{Bolt in the front of the hotel, New Ross, above 1 f By 

 the bolt at Buckingham Lock, Dublin J I By 



{Mark at Lord Glengall's house, Cahir, below 1 / By 

 bolt in Monasterevan Church I I By 



r Bolt in Penrose Quay, Cork, below mark on 1 J By 



L William Street Bridge, Waterford J I By 



/ Mark on Mead's Quay, Limerick, below mark t J By 



L at Court House, Borris-in-Ossery J \ By 



/ Mai-k on Tralee Bridge, below mark on Holy- 1 f By 



\ cross Bridge J L By 



J Bolt in Loughrea Church, above the bolt at \ f By 



[ Buckingham Lock, Dublin J I By 



/ Mark on Oranmore Bridge, above mark on 1 J By 



\ Mead's Quay, Limerick J \By 



r Bolt in the Market House, Armagh, above the "1 f By 



L bolt at Buckingham Lock J L By 



J BoltinthefrontofCommercialBuildings, Belfast, 1 J By 

 \ below bolt on Sugar Island Bridge, Newry... j \ By 

 f Bolt in Port Rush Pier, below bolt in Commer- 1 / By 



\ cial Buildings, Belfast J I By 



J Bolt in Castlebar Gaol, below mark at Kin- \ f By 



L negad J JBy 



J Bolt in Commercial Buildings, Belfast, below 1 f By 



\ the bolt at Buckingham Lock J I By 



J Mark at Londonderry Bridge, above bolt at "I J By 



\ Buckingham Lock J I By 



J Mark'at Cliflfony, near MuUaghmore, above bolt 1 f By 

 \ at Buckingham Lock J I By 



Monasterevan 



Gorey 



Borris-in-Ossery 



Waterford 



Cahir 



Dungarvan 



Nenagh 



Holycross 



Limerick 



Cahir and Mallow 



Ballinasloe 



Nenagh 



Nenagh 



Kilrush 



Dundalk and Newry 



Navan, Cavan, Newtown Butler and Monaghan 



Armagh, Portadown, and Lisburn 



Downpatrick and Newtown Ards 



Glenarm and Ballycastle 



Antrim and Coleraine 



Longford, Ballysadare and Ballina 



Ballinasloe and Tuam 



Newtown Butler and Armagh 



Newry, Downpatrick and Newtown Ards 



Newtown Butler, Monaghan and Strabane ... 



lines round the east and north coasts 



Newtown Butler and Ballyshannon 



Kinnegad and Ballysadare 



101 



84 



72 



110 



95 



85 



50 



68 



105 



122 



108 



130 



76 



109 



82 



118 



58 



62 



83 



62 



140 



122 



156 



125 



168 



243 



139 



145 



Difference of level 



«- 



ft. 

 10 



11 



48 



48' 



3 



3 



348' 



347 



272 



272 



268 



268 



?■ 



8 



146 



147 



5 



4' 



6 



6 



98 



98 











2 



•698 

 •469 

 203 

 796 

 471 

 973 

 344 





ft. 



11-826 



11397 



48-482 



47053 



3-257 



4015 



347-465 



•661347-940 



•5 75 1273-262 



389,272-920 



•558 268-.993 



76> 

 573 

 341 

 771 



•970 

 327 

 334 



•589 

 •795 

 •486 

 •269 

 •828 



268-519 

 7-981 

 7-886 

 ... 147146 

 061146-561 

 477! 5-489 

 6-109 

 5-086 

 6-893 

 98-341 

 99-110 

 1-087 

 1-122 

 2-351 



998 

 520 



93117 

 94-314 



CO r- 



o<S.g 



5* 



ft 



1-128 

 0-072 

 0279 

 1-743 

 0-214 

 0-042 

 0-879 

 0-279 

 0-687 

 0-531 

 0435 

 0-243 

 0-408 

 0455 

 0375 

 0-500 

 0012 

 1-139 

 1-241 

 0-559 

 0-248 

 0315 

 0601 

 0-853 

 0-477 



0-881 

 1-794 



Its 



S 



ft. 



11-262 



11-433 



48-342 



47-924 



3-364 



3-994 



347-904 



347-800 



272-918 



272-654 



268-775 



268-640 



7-777 



8-113 



146-958 



146-811 



5-483 



5-539 



5-706 



6-614 



98-465 



98 952j 



0-786 



0-695 



2-589 



3-647 



93-557 



93-417 



2| 



O 'ti 



Is 



ft. 

 }■ 0-171 



1 0-418 



1 0-630 



U-:04 



1 0-264 



1 0-135 



j 0-336 



|o-147 



1 0-056 



1 908 



1 0-487 



1 0-091 



1 1-058 



j 0-140 



On these results, the following remarks are made by Colonel Colby. 



The discordance in No. 10 is unusally great; but as it appears from an examina- 

 tion of the levelling that the error in discordance is of gradual accumulation and 

 does not arise from any one mistake, the mean of the two results is adopted for Port 

 Rush, and a part of the difference between this mean and the result on either line, 

 proportional to the distance of any point on that line from Belfast, is adopted as a 

 correction for the apparent elevation of such point. 



In No. 13, second line, the comparison of forward and backward levelling is 

 omitted, the principal part (namely that from Dublin to Port Rush) being contained 

 in Nos. 10 and 12. The mean of the two results for Londonderry was adopted ; upon 

 this depend the zeros of Carrowkeel and Buncrana. 



The station at Limerick being important, its relation of height to that at Dublin 

 was ascertained by four different lines. The following Table contains the results of 



