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Bob VanderPol

You asked, "tell me about HO 203/204"

Okay, here goes!

My volume of HO 203 was published in 1923 and has several 'pasted in' corrections, denoting active use of the volume and interest by the Hydrographic Office in staying current.  My volume of HO 204 was published in 1933.  Somebody was buying and using these volumes.  That's a ten year span of publication and updates, at a minimum.

The two volume set is just about 1,600 pages long.

The title of HO203 is as follows:

"The Sumner Line of Position furnished ready to lay down upon the chart by means of tables of simultaneous hour angle and azimuth of CELESTIAL BODIES; Latitude 60°N. to 60°S. - Declination 27°N. to 27°S."

It just rolls off the tongue!!

The title of HO204 is as follows 

"The Sumner Line of Position furnished ready to lay down upon the chart by means of tables of simultaneous hour angle and azimuth of CELESTIAL BODIES; Between 27° and 63°of Declination; Latitude 60°N. to 60°S."

So we end up with a monolithic table for latitude +/-60° and declination from 0 to 63°.

There are some preliminary tables inside, like (Table 1) Height of Eye combined with refraction and (Table 2)the moon's HP, but the main table consists of the following

For each degree of latitude and whole degree of declination, as a function of the true altitude from 5° upwards to, at times, 90° the resultant hour angle (h.m.s) and azimuth is provided.  Interpolation help is also provided with the difference in each 1' of declination for hour angle and azimuth.

The table is bifurcation into Same Name / Contrary Name, when we consider the latitude and declination names.  The table may be viewed at link at hathitrust.org.

Examples of how to use the tables, complete with plotting charts are shown in the text.  Readers will immediately recognize modern line of position navigating. 

To support my contention of early tabular method, HO 203 specifically credits the  predecessors of the work.  Attached is the only image, as the Hathitrust.org image was a smudge of these tiny characters.

Note particularly that the author credits works of 1793, 1827 and 1829. These all predate Sumner.  If there were other tabular predecessors, you might think the author would have noted them.  Alas, he did not.  Now why is that?  To avoid being accused of plagarism?  To give proper technical credit?

But why no other, more modern tables?  Is this the first?  I make no such claim.  The author does state that "It is evident that IF the solution of [spherical triangle angles] are tabulated corresponding to all the usual values of these three sides of the [spherical] triangle, there will be no need of any calculation and hence, that a simplification is afforded in obtaining the data for drawing the Sumner Line by the accompanying tables".  I've added emphasis to the "if", but the sentence is written as if the idea of a table was a new development.  Which would indeed make it a first if true!

I look forward to being corrected on this point of early tabular method.  Stan, you mentioned some tabular methods in passing without identifying them, so please?

 The tabular method presented in HO203/204 is a solution to the spherical triangle by table lookup.  It is NOT a table of 10+log10 (trig function) that we observe in Time Sight Navigation.  It is a true spherical triangle lookup, very similar to 249 and 229 in concept, albeit not is specific detail.

Brad