258 
Proceedings of the Boyal Society 
tor) ; but as lie only gives tbe totals in this way, the details must be 
sought in the typographical edition of his work called The Travellers 
Guide For comparing the “computation,” “vulgar com- 
putation,” or “reputed” miles, with the real distances, Ogilby’s 
statute miles have been here adopted, as he has no constant error in 
one direction, and his fluctuating errors are much less than those of 
the reputed miles, so that no further inaccuracy will be caused by 
taking his statement. In this investigation the roads were broken 
up into lengths of about forty miles each for purposes of com- 
parison of the mile lengths ; and besides this, there are shorter 
lengths of cross roads. The lengths compared together are in all 154 
in number, of which 134 belong to the old mile, eight to the N.W. 
mile, and twelve to the Welsh mile. From the mean of these 134 
lengths, the old mile appears as 1307 ± 5. The local miles we pass 
over for the present ; but the posting miles which are given, though 
agreeing in general with the old miles, yet in nine cases are shorter, 
and in two cases a little longer ; the shortest form is equal to the 
statute mile. 
From Ogilby’s work lists of miles were reprinted more or less 
abbreviated, as in the The Complete Tradesman, by IST. H. (1684), 
which gives both “computed” and “measured” miles. In 
The Exact Dealer, by J. H. [John Hill] (1688), the miles are 
generally the reputed or long miles of Ogilby, but sometimes the 
post miles, or others. In The Description and Use of two 
Arithmetic^ Instruments, by Sir Samuel Morland (1673), just 
before Ogilby’s publication, the miles are the same as the post 
miles in Ogilby, where they differ occasionally from Ogilby’s 
reputed miles. 
The next earlier information is in the maps of Eugland com- 
monly known as “The Quartermaster’s Map” (1644). This gives 
a scale on each of the six sheets ; and on measuring two distances 
on each sheet to obtain the absolute value, it appears that these 
maps are far more accurate than any others of that period, the 
average error being but a third of that of Saxton, Speed, or Gibson. 
The mile value from this source averages 1255 ±10. 
In the year before this A Direction for the English Traveller 
* This is catalogued under Ogilby in Brit, Mus. ; but he died in 1676. 
There is no editor’s name to it. 
