Crosses, Numerals & Spoons. 
After creating stamps in use for postage in 1840, it was necessary to cancel them to prevent reuse. The Maltese Cross cancels did the job, but there was a need to know where a letter was mailed. These cancels vaguely resembled a Maltese cross, hence the name, but MacKay notes they looked more like flowers than crosses. The Cross cancels can be identified to a some post offices, but only with difficulty and certainly don’t tell when. (Figure 1)
If one assigned an alphabetic list of the telegraph offices a numeric code each, then the problem should be solved. Or would it? Kingston, England and Kingston, Ireland share the same name along with many other places although different numbers. Some clever person changed the shape of the cancel border. We can make an oval border for English locations, a rectangular box of parallel lines for Scottish ones, and a diamond shaped one for those in Ireland. Now lets put the number in the center. Does this solve the problem? (Figures 2-4).
It seems like the English explorers and cartographers had a propensity for naming places in the colonies for places in the British Isles. So, we have Kingston, Jamaica, Kingston, Canada, Kingston, Pennsylvania, and Kingston, Long Island, and a few more. We can drop the Americans from the list, and the Canadians use a different system, but Jamaica uses the standard British system, so we’ll have to add a letter to the number, and since Kingston is the Jamaican capital, make it A01. (Figure 5).
The Irish design of the diamond background was another problem for the Numeric Cancels. The number of lines in the diamond varied. Sometimes 6 above, four partial lines where the station number was and 6 below (6,4,6).[Belfast #62] (Figure 6) Other combinations were also in use. (Figures 7: 3,3,3[Killiney #273] & 8: 8,5,8 [Limerick #303]) Reducing the number of lines prevented ink buildup on the thinner lines. Cancels are known with as many as 8 lines above and below and 5 in the middle. Figure 8 shows a numeric cancel on cover. (Figure 9).
Initially, the station numbers ranged from 5 to 450 with some numbers omitted to avoid confusion if inverted. Thus19 was used while 61 was not. Of course, as soon as the Post Office opened a new office, the numeric sequence integrity was lost if placed alphabetically, or vice versa. We can add letters to the Numeric cancels, but now the legal system is demanding a clear text identification of not only where, but when the letter was mailed. This was resolved by having the postmen use a second stamp with the town name, date and time. Since mail volume had been continuously increasing, having to use two different stamps slowed the process. So, lets make one stamp incorporating both.
The Spoon cancel with location, date and time spelled out clearly for all to see. Numeric cancels were used until the late 1850’s, and were slowly phased out. The spoon cancel was a further development of the Numeric cancel. Now, the diamond shaped background of parallel lines was used with the telegraph station number in the center, but now with an added circle to the left contains the town name, the date, and the time and the cancel letter or number. ( Figure 10). This was a large cancel, and the full effect can only be seen on this cover from Bray.
Collect British Postmarks by Dr. J.T. Whitney and published by the British Postmark Society is one of the most useful references to this interesting genre. Chapters 5-7.
The Stanley Gibbons Commonwealth Catalog, Stanley Gibbons, Ltd, along with other Gibbons catalogs cover the number system in the Foreword.
Irish Cancels Since 1840, MacKay, J., Chapters 2, 3.