A 



1311 HYDROGEAPHIC MANUAL PaGE 16 



surveys, with which junctions are to be made, will always be furnished, as well as 

 copies of the most recent ones of the entire area, if the latter are believed to be helpful. 



\Vlien inshore hydrographic surveys are to be made after air photographic surveys 

 of the area have been completed, printed smooth and boat sheets may be furnished, 

 or tracing paper prints or ozalid prints will be furnished from which to transfer the 

 shoreline and control points (see 733). Lithographic copies of planimetric maps 

 within the area will be furnished as well as copies of the field prints of the photographs 

 if the latter are believed to be of value in connection with the operations. 



If any of the survey data are confidential, the Chief of Party shall be responsible 

 for their custody and for their eventual return to the Washington Office (see 125). 



7377. Photographic Copies of Field Data 



When the Chief of Party has reason to believe that the data furnished with the 

 instructions are not complete, he should notify the Washington Office immediately, 

 requesting the additional data. If, during the course of his field operations, copies 

 of additional field data are found to be desirable they should be requested from the 

 Washington Office in ample time for the photographic reproductions to be made and 

 forwarded to him. Usually either photostat or bromide copies of field data are 

 furnished. 



1312. Photostat Copies 



Photostats made in the Washington Office are limited to a paper size of 18 by 24 

 inches and to a subject size of 17 by 22 K inches; a reduced photostat is ordinarily 

 limited to no smaller than one-half the scale of the original; and an enlarged photostat 

 is ordinarily limited to no larger than twice the scale of the original. A photostat is 

 normally a negative in that the black and white of the original is reversed but the copy 

 is otherwise correct. Positive photostats may be made from the negatives and have 

 white backgrounds. 



When a request is made for a photostat, a negative will always be furnished unless 

 a positive photostat is specifically requested and the reason for the need for the latter 

 is given. Photostats cannot be relied on to be at correct scale, and when such copies 

 are used for the transfer of shoreline or control stations, extreme care must be used. 

 If the quadrilateral formed by the meridians and parallels enclosing the area in ques- 

 tion is measured, and found to check with the values in the Polyconic Projection 

 Tables (see 7321), it is safe to assume that the details within that area are true to scale. 



7373, Bromide Copies 



When photographic copies larger than 17 by 22^2 inches are required, bromide 

 copies are usually made. A bromide is made by first photographing the original at a 

 reduced scale on a glass or film negative, and then making an enlargement on bromide 

 paper, usually at approximately the same scale as the original. The bromide paper 

 does not come in contact with the negative. Since the size of most survey sheets, 

 except aluminum-mounted sheets, is at least 31 by 52 inches, bromides are necessarily 

 made when copies of entire surveys are required to scale. They are limited in size to 

 38 by 72 inches. 



A bromide can be made approximately to any desired scale. It is one of the most 

 unsatisfactory of all copies insofar as clarity and true scale are concerned. Bromides 



