86 PROCEEDINGS OF THE CALIFORNIA 
made in getting an exact coincidence of the images of the signals is then less 
felt by the angles than if the signals were near or the angles very acute. 
And besides what is thus told by the relative positions of the signals, the 
hydrographer should be able to read the tale which the size of the observed 
angles tell’of a position’s fixedness. If the sum of the observed angles equals 
180 degrees or more, then the observer is sure he is not on the circle of 
indetermination. But if this sum is less than 180 degrees, and equal, or 
nearly so, to the supplement of the angle subtended at the middle signal 
by the other two, then the position is not determined. By having these 
supplements written about the signals, between the proper lines, on the field- 
sheet, we can by a mental summing of the observed angles tell (without 
plotting) whether we are too near the circle to get a good determination; and 
may thus catch other angles that better fix our position. 
The three-point problem finds in the three-arm circular protractor an accu- 
rate, simple and most expeditious graphic solution, which is most extensively 
used in plotting positions of the sounding-boal. In practice the observed 
angles are set off on the proper lines of the protractor, and the fiducial edges 
of its arms caused to traverse the three points representing the signals 
observed upon, and the center dotted, and the position is plotted. If breakers 
denoting danger be observed at a time when it is impossible to anchor over 
them, or even approach them to fix a buoy to mark their locality, their position 
may be marked quite accurately by pulling around them and getting cross 
ranges (or cross magnetic bearings) of prominent objects on shore, so dis- 
posed as to guide the observer to the spot in more favorable weather, when a 
perfect calm may leave no trace whereby the danger can be recognized. 
Henry Edwards submitted the following: 
Pacific Coast Lepidoptera, No. 11.—List of the Sphingidze 
of California and Adjacent Districts, with Descrip- 
tions of New Species. 
BY HENRY EDWARDS. 
As the value of local lists is fully recognized by entomologists, I propose, 
in the present paper, to furnish a complete catalogue of the species of this 
interesting group of Lepidoptera, as far as known to me to inhabit the Pacific 
Coast, and to offer descriptions of what appear to me to be forms as yet un- 
recognized by science. The number of species, compared with those of the 
Eastern States, is but small, but extended exploration of our little known 
mountains and valleys may furnish us with others, while it is more than 
probable that many of those from Northern Mexico may yet be found within 
our borders; and, acting upon this belief, I have introduced the description 
of an exquisite species from the region of the Sierra Madre, which may some 
day have to be included in our lists. I have followed the arrangement pro- 
posed by Messrs. Grote and Robinson in their catalogue of Lepidoptera, 
(No. 1, Am. Entom. Soc., 1868,) and have invariably adopted the generic 
