Commentary
This passage officially confirms Grassmann as mad as I am! And of course I love it!
There is no teacher of Maths on this earth who would tell you this passage is correct! In fact Robert, Hermann's own brother made sure not to copy this passage into the 1862 version of Hermanns Ausdehnungslehre(redacted!) .
Robert strongly steered Hermann away from these kinds of "mathematical" identifications, onto s strictly formal system acceptable to most mathematicians. This stuff was definitely not for Möbius or Gauss. The formulae Grassmanns method gives rise too were undeniably correct or well known, but the method of derivation was highly questionable, highly mystical and highly unusual!
The reputation for obscurity derives from passages like this.
I disagree that they are obscure. In every instance Grassmann tries to make it crystall clear. But they fail to communicate to those taught to think only in certain ways, or more accurately to write their conclusions in a formal set up.
It is interesting to see how tentatively Mathematicians finesse this piece of historical lore in the development of the hyperbolic descriptors.
http://www.youtube.com/v/er_tQOBgo-I&rel=1&fs=1&hd=1There are many other brief introductions into the lore, but no one really goes into it too deeply! It is presented as a confusing mnemonic scheme. However all trigonometric ratios are usually taught heavily using a mnemonic structure. SOHCAHTOA is just one mnemonic for the sine ,cosine and tangent ratios..
What is really going on here?
For centuries, at least from the 5 th century AD astrologers had been calculating improving and recalculating the Sine trigonometric ratio for the Bow or the Indian half Bow. The Persians made great headway based on the Greek research into the Babylonian records, but the Indians made the greatest innovations based on the Greek astrological ideas, introducing the great simplification of the radius and the half chord forming the half bow.
However it was the Arabs who collated all the best work together nd set in motion a centuries long calculation of the sines to many figures of accuracy.
Without these tables and the ongoing research, the differential formulae for interpolation would not have been invented. The ratios of the diminishing proportion would not have been investigated by Napier leading to his logarithms of the sines and mercators conundrum for map projections would not have been solved logarithmically.
Finally the evident applicability of the method of Fluxions would not have suggested itself in formulaic terms to Newton, Wallis et al , nor would Newtons mastery of the Multinomials establishing his development of the binary series expansion have been so sweetly done!
In fact De Moivre who took time to study every page of Newton often astonished fellow scientists by his ease in solving Multinomials with large factors! Both he and therefore Newton knew the numbers were in the sine tables, the Multinomials in the differential formulae for interpolation, and the calculus in them both!
Because of the binomial series and the coefficient, de Moivre made probability his life's work, again relying on the resource of the sine and logarithm tables.
However, the Cotes deMoivre theorems for the roots of unity was perhaps his greatest uncontested achievement!
Based on principles and ideas laid down by Newton, de Moivre solved many difficult Multinomials using the
. In particular he factorised the cosine and sine sum to find roots for the circle equation.
While he found many useful answers in this way it was Sir Roger Cotes who , faced with the problem of calculating the rhumb line for navigators , on inquiring of De Moivre found a remarkable and important use for these methods of De Moivre.
Together they collaborated to definitively expound on this trigonometric solution to the circle equations. The Cotes De Moivre theorem is a remarkable piece of calculation based on the sine and haver sine tables, or the cosine tables that were beginning to appear.
Cotes took it one stage further and made the discovery that the constant magnitude
was indivisibly associated with the quarter arc! He devised an alternative measurement method for the unit circle based on the ratio between the arc length and the radius. This meant he could write down a length, associate it to an arc and then tabulate the sine or cosine for that arc. No right triangles were necessary, but of course they are indivisible from the circle in any case..
With this method he could now rewrite the logarithm of sines in terms of arc lengths. Using Newtons logarithmic series he was able to demonstrate the remarkable equation or identity
Essentially the arc length is related logarithmically to the sum of the trig ratios in the form written where i is eulers definition .
He died before he could explain this to Newton, and before De Moivre to get up to speed with his research.
He had written an important identity derived from an equation with infinite terms!
The whole idea was preposterous. Parmenides and Zeno were invoked! But the fact of the matter is, ignoring the equation , the identity related very different ratios together in a consistent and robust way. This was an implicit formulation. Actual values could not be sensibly equated, but actual values were sensibly calculated!
What was going on?
The answer lies in our subjective processing.
We can and routinely do calculate in parallel. To survive , many parallel calculations occur simultaneously, and results are applied to the solution by the various subsystems that require it.
However, most mathematicians are not trained to calculate in this way, and indeed there was no notation, logarithm or method explicitly designed to emphasise this, except long division!
Most of us who still do long division organise our calculations after the Indian methods. In so doing we do multiple calculations in parallel and in a highly spatially organised way, on the page.
We are not taught to see these long divisions as linear combinations of products! Neither are we taught to recognise the spatial disposition as separate operations.
Writing out a long division as a combination of products would organise them into a series of products arranged geometrically. In the case of division the connectors or conjunctions would be mainly minus and the coefficients would be the figures usually written atop the division box.
Thus all divisions are some form of geometric series, that is a large sum, and contrariwise all products are some form of geometric series, that is a large sum!
So returning to votes, his identy reflects the fact tht our calculations are the results of large summations. The fact that the summations may be infinite is not an issue if one can identify when to stop! This is a practical decision. It can of course be ndlessly debated, but pragmatics has the answer to Parmenides and Zeno.
So, realising this astrologers used Cotes method. They examined the hyperbolic curve using the sine tables. The sine tables were and are a reliable resource. If a curve can be described using them, then many techniques if analysis are available to the astrologer.
When the curves were examined it became clear they had to be flipped by a quarter turn, because the sine goes from 0 to 1' and in addition 1 had to be added to the values.
Well Napier showed how the logarithm of sines could be calculated on diminishing proportions from 1 and the hyperbolic require increasing proportions from 1. By this time everyone knew the exponential growth calculation for compound interest! Both Citrs and Newton and DeMoivre calculated this logarithmic base ratio to about 20 decimal places. It was 2.718...they knew this ratio, they calculated the logarithms of this ratio after the manner of Napier, that is why they are called Napierian logs or natural logs ( to distinguish from the logarithm of one's, and the later logarithms of Briggs) and they were used mainly by actuaries in the calculations of life insurance etc.
Decades later Euler sets out the identities in all clarity, but by then many did not recognise the summation nature of all products, even when Euler was pushing their faces into it.
Grassmanns foible now makes historical and radical sense.