I20 ' DISCOVERY REPORTS 



in his continued interest in the progress of the work ; to him we owe a translation of 

 Schott's recent writings. I am indebted to Miss D. M. E. Wilson for titrating the 

 water samples and to Miss E. C. Humphreys for the care she has taken in preparing 

 the figures for reproduction. Among the many others who have helped I wish to thank 

 especially Dr C. E. P. Brooks and Dr J. A. Fleming, Mr E. W. Barlow, Mr G. E. R. 

 Deacon, Dr T. J. Hart, Mr G. R. Crone, and Miss E. I. Holme. In particular, I am 

 indebted to Dr S. W. Kemp, whose help and sympathy have greatly facilitated the 

 execution of the work. 



The Carnegie Institution of Washington has kindly supplied manuscript data of the 

 ' Carnegie's ' cruises in the Pacific ; the Admiralty and the Royal Geographical Society 

 have extended library facilities, and the Meteorological Office has loaned daily weather 

 bulletins of Chilean Meteorological Stations. 



EQUIPMENT AND METHODS 



Winter months were allotted to the survey because the R.R.S. ' William Scoresby ' was 

 due to work in the south during the southern summer ; there was otherwise no special 

 design in choice of season, though it was hoped that by compressing the work into a 

 relatively short space of time symmetrically arranged about the winter solstice 

 uniformity in weather conditions and temperature might be secured. 



The ship at first under the executive command of Lt.-Comdr. J. C. C. Irving, R.N. 

 (Retd), and later of Mr F. E. C. Davies, cruised over the whole area from the Gulf 

 of Penas to Santa Elena in Ecuador. On the northward journey from May i8 to July 

 26 she carried out the greater part of her programme, working eleven lines of stations 

 across the path of the current in the space of two months (Figs. 2 and 3). The return 

 journey southward was made the occasion for an additional line off Santa Elena and 

 for working oceanic stations in a meridional direction and for repeating the observa- 

 tions made off Callao in July. The ship steamed on a direct course from the Callao line 

 to Pichidanque Bay. 



Two objects were kept in view in planning the positions of stations: firstly the 

 securing of a sufficient number of observations to provide data for hydrological sections, 

 and secondly to span the breadth of the current. The first station of each line was 

 placed as close as possible to the shore. Owing to isothermal irregularity the stations 

 over shallow water were placed close together, but those following, over deep water, 

 had to be placed at progressively greater intervals. Each line was terminated when 

 the isotherms beneath the surface showed a horizontal tendency. This point on the 

 line, dictated by considerations of economy, might or might not approximate to the 

 western boundary of the Peru Coastal Current, but it always lies between the cooler 

 inshore waters, where upwelling and coastal influences cause isothermal irregularity, and 

 the open ocean, where the surface water is warmer and where the temperature shows 

 a condition of comparative stability. 



When running from one station to another on the same line, the ship was usually 



