Lesley.] 6^ [jan. 15, 



A beginning lias now been made in Pennsylvania ; and 

 the following pages contain the records of the height above 

 some assumed datum, reduced to tide level, of all stations on 

 railways in the State, and in its immediate vicinity. 



These records have mostly been obtained by personal 

 examination of the profiles preserved at the offices ; and in 

 some cases, by letter, from superintendents and engineers. 

 The greatest interest in the Collection has been manifested 

 by members of the profession of Civil Engineering to whom 

 application has been made ; and in some instances, where 

 records were wanting, new levelings have been ordered and 

 the results transmitted. 



Short headings are prefixed to the records, stating place, 

 date and authority ; and foot notes appended to them, 

 stating difficulties of adjustment, incongruities, or doubts. 



That a work of this nature should have the advantage of 

 first publication in the transactions of the oldest Scientific 

 Society of America, whose first President was Benjamin 

 Franklin, and whose hall stands side by side with the 

 ancient Capitol of the United States, is my reason for 

 asking that this first systematic attempt on a large' scale to 

 render permanent and useful to all engineers and surveyors 

 the scattered and perishable records of heights above sea- 

 level of several thousand points in our valleys and on our 

 mountains should be accepted by the Society. 



It must be understood, however, that these lists require 

 thorough rc-examination and correction before they can be 

 adopted as constants of science for the future. There are 

 considerable difficulties yet to be encountered by such as 

 undertake to harmonise the data of our railway surveys. 

 Indeed, considering the imperfect way in which such surveys 

 are necessarily made, — the accumulation of errors of instru- 

 mentation and pei-sonal equation along every long spirit- 

 level line, — the uncertainty even of the tide-level datum at 

 every head of tide, — the frequent lack of notes stating 

 whether railway levels cross each other on grade, or not, — 

 and the not uncommon fact that, after location-surveys have 



