218 report — 1877. 



On the Difference of the Steering of Steamers with the Screw reversed when 

 under full way and when moving slowly. By Professor 0. Reynolds, F.R.S. 



On a more extended use of the Ordnance Datum of Great Britain. 

 By J. N. Shoolbred, Mem. Inst. C.E. 

 At a time when a committee of the Association presents a Eeport * to endeavour 

 to dispel certain misconceptions as to the meaning and true position of the Datum- 

 plane selected as the basis of the levels of the Ordnance Survey of Great Britain, it 

 may not be inappropriate to ask the question, whether this Datum cannot be more 

 fully made use of, so as to become what it ought to be, a truly national basis or 

 connecting link between all works of a public character throughout the entire 

 length and breadth of the country ; and also by what means this can most readily 

 be efFected. It would appear, inter alia, that much would be done if this basis 

 of the system of Ordnance Levels were connected: — 



1. In towns with all surveys of Municipal and other bodies. 



2. In seaports and harbours with dock-sills, tide-gauges, and marine surveys of 

 the port and of the adjoining coast, thus enabling tidal observations in different 

 parts of the kingdom to be compared with one another. 



3. With existing local datum-marks. 



4. On Railways and other large public works with their system of levels as 

 given in their deposited plans before Parliament, so as to allow of the different 

 works, or their several portions, being connected together. 



As, in order to give force to this last recommendation, an addition to the Stand- 

 ing Orders of both Houses of Parliament woidd be requisite, memorials to the 

 Chairman of Committees of each House from such bodies as the Council of the 

 British Association, of the Institution of Civil Engineers, of the Institution of 

 Surveyors, of the Society of Arts, of the Geographical and of the Geological 

 Societies, and of others having kindred objects, might be productive of the desired 

 effect. 



The whole of the foregoing remarks, it need hardly be said, apply with equal 

 force to the Datum of the Ordnance Survey of Ireland. 



It may also here be noted that the Ordnance Department is itself doing much, 

 in the direction indicated by the foregoing remarks, by the issue, now being made, 

 of the Parish maps (25 inches to the mile). They supply similar information to 

 that contained in the several Tithe-Commutation Parish maps ; and besides they 

 are studded with levels of the country tliey represent. Thus they afford ample 

 requisites for a good estate-map, and as such they promise to become both valuable 

 nnd duly appreciated. 



On a Suspended Railway. By G. Stevenson. 



On the Importance of giving a Distinctive Character to the Needles Light. 

 By Sir William Thomson, F.R.S. 



On an Improved Method of Recording the Depth in Flying Soundings 

 By Sir William Thomson, F.R.S. 



On a Navigation Sounding Machine for use at Full Speed. 

 By £ir William Thomson, F.R.S. 



On the Mariners Compass, with Correctors for Iron Ships. 

 By Sir William Thomson, F.R.S. 



See p. 200 of the present volume (Reports). 



