CONTENTS.

PART I.

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1-15

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15-26

Major-General Colby's character and appearance. An-
cestry. Education. First connection with the Survey.
Terrible Accident at Liskeard.
Major-General Roy on Surveys. Survey in 1747. Funds
supplied for a Survey by George III. Modes of Mea-
suring. Survey under General Roy. Duke of Richmond,
Master-General of the Ordnance. Survey under Lieut.-
Colonel Williams. Triangulation from the Isle of
Thanet to the Scilly Isles
Marquis of Cornwallis, Master-General. Survey under
Captain Mudge. Ramsden's Sector. Determination
of an Arc of the Meridian. Result questioned by
Rodriguez..
Publication of Proceedings. The Survey extended North-
wards. Inquiry of the Military Commissioners.
Expenses
Prolongation of the Meridional Line into Scotland. Pro-
fessor Playfair's remarks. Mineralogical Survey. Vindi-
cation of Ramsden's Sector. Geodesical and Astro-
nomical determination of Arcs. Professor Inghirami's
difficulties. Difficulty of determining Latitudes.
Soldiers employed on the Survey. Comparison of
Standards and Meridional Arcs...

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Captain Colby's remarks on Edinburgh Observatory.
Comparison of Base Lines. Instruments used on the
Continent. French and English Arcs: observations in
Shetland
Pendulum Experiments. Instantaneous Signals

40-59

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93-105

105-119

Publication of Maps. The Sector at Dunkirk. Major
Colby's skill as an observer
Death of General Mudge. Captain Colby appointed
Superintendent of the Survey by the Duke of Welling-
ton. Operations for connecting the Meridians of
Paris and Greenwich. The Compound Lense, Helio-
stat, and Theodolite
Officers employed on the Survey. The Irish Survey.
Manx Hospitality. The Camp on Divis. Personal
superintendence of the great Triangulation confided to
Colonel Portlock. Colonel Colby's visits to country
stations. Observatory at Culeagh
Scotch Survey resumed. Major Dawson's account of a
year on the hills. Perfection of the English Map 131-158

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120-130

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159-180

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180-194

194-208

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209-215

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PART II.

Objects of previous and projected Surveys. The Down
and Strafford Surveys
Scale of the Down and Ordnance Surveys. Remarks on

various scales
Mode and importance of determining Boundaries and
Names of Places. Mode of Survey. Duty of Calculating
separated from that of Observing. District triangula-
tion. Acreage
New System of Altitudes, advantageous to Farmers and
Engineers. Effects of Refraction
Map of proposed Railways. Introduction of Contour
lines. Expression of Altitudes by Contouring and by
shading
Soldiers employed. Sappers useful as observers...
Importance of office arrangements. Efficiency of the

office in the Phoenix Park under Lieutenant Larcom.

Plotting. Computing. Meteorological observations.
Engraving. Printing. The Force employed on the
Irish Survey

223-240

PART III.

Estimation of the

General Colby as a man of Science.

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241-247

247-257

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257-277

Earth's dimensions by Eratosthenes, Posidonius, Pto-
lemy, the Caliph Abdalla Almamoran, Fernel, Snell,
Norwood, Riccioli, and Picard ...
Newton's theory of Universal Gravitation. Arcal mea-
surement in France, Peru, Sweden, and other coun-
tries
Measuring Rods and Chains. Experiments at the Tower.
Colby's Compensation Bars
Compensation Bars used for the measurement of Lough
Foyle Base, on the Indian Survey, and at the Cape of
Good Hope
Respective merits of the Repeating Circle and Theodolite 280–289
Objects for Observation. The Heliostat. The Lime

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Light
Method proposed by Baron Zach for Base measurements.
Disturbing effects of local attraction. Airy's Sector 294-302
Review of General Colby's and General Roy's services and

ROYAL OBSERVATORY, GREENWICH,

LONDON, S.E.,

1869, June 9th.

MY DEAR MADAM,

THE number of occupations which have pressed upon me about the time of the Annual Visitation of the Royal Observatory have made it almost impossible for me to write a private letter. This is the explanation of my long delay in answering your letter of May 22.

I have perused, with some attention, Colonel Portlock's Memoir. I need not say that it contains much with which I was not sufficiently acquainted to have been able to write anything with certainty. But all that I do know is given with great accuracy and fidelity, and a generally correct idea of the remarkable man who is the subject of the Memoir will be obtained by reading it.

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