(source) 
Peter Guthrie Tait
(28 Apr 1831  4 Jul 1901)

Science Quotes by Peter Guthrie Tait (6 quotes)
If it were possible for a metaphysician to be a golfer, he might perhaps occasionally notice that his ball, instead of moving forward in a vertical plane (like the generality of projectiles, such as brickbats and cricket balls), skewed away gradually to the right. If he did notice it, his methods would naturally lead him to content himself with his caddies’s remark“ye heeled that yin,” or “Ye jist sliced it.” … But a scientific man is not to be put off with such flimsy verbiage as that. He must know more. What is “Heeling”, what is “slicing”, and why would either operation (if it could be thoroughly carried out) send a ball as if to cover point, thence to long slip, and finally behind backstop? These, as Falstaff said, are “questions to be asked.”
— Peter Guthrie Tait
It is very desirable to have a word to express the Availability for work of the heat in a given magazine; a term for that possession, the waste of which is called Dissipation. Unfortunately the excellent word Entropy, which Clausius has introduced in this connexion, is applied by him to the negative of the idea we most naturally wish to express. It would only confuse the student if we were to endeavour to invent another term for our purpose. But the necessity for some such term will be obvious from the beautiful examples which follow. And we take the liberty of using the term Entropy in this altered sense ... The entropy of the universe tends continually to zero.
— Peter Guthrie Tait
Nothing can he learned as to the physical world save by observation and experiment, or by mathematical deductions from data so obtained.
— Peter Guthrie Tait
The flights of the imagination which occur to the pure mathematician are in general so much better described in his formulas than in words, that it is not remarkable to find the subject treated by outsiders as something essentially cold and uninteresting— … the only successful attempt to invest mathematical reasoning with a halo of glory—that made in this section by Prof. Sylvester—is known to a comparative few, …
— Peter Guthrie Tait
We are quite ignorant of the condition of energy in bodies generally. We know how much gas goes in, and how much comes out, and know whether at entrance and exit it is in the form of heat or of work. That is all.
— Peter Guthrie Tait
Your printers have made but one blunder,
Correct it instanter, and then for the thunder!
We’ll see in a jiffy if this Mr S[pencer]
Has the ghost of a claim to be thought a good fencer.
To my vision his merits have still seemed to dwindle,
Since I have found him allied with the great Dr T[yndall]
While I have, for my part, grown cockier and cockier,
Since I found an ally in yourself, Mr L[ockyer]
And am always, in consequence, thoroughly willin’,
To perform in the pages of Nature's M[acmillan].
Correct it instanter, and then for the thunder!
We’ll see in a jiffy if this Mr S[pencer]
Has the ghost of a claim to be thought a good fencer.
To my vision his merits have still seemed to dwindle,
Since I have found him allied with the great Dr T[yndall]
While I have, for my part, grown cockier and cockier,
Since I found an ally in yourself, Mr L[ockyer]
And am always, in consequence, thoroughly willin’,
To perform in the pages of Nature's M[acmillan].
— Peter Guthrie Tait
Quotes by others about Peter Guthrie Tait (5)
That small word “Force,” they make a barber's block,
Ready to put on
Meanings most strange and various, fit to shock
Pupils of Newton....
The phrases of last century in this
Linger to play tricks—
Vis viva and Vis Mortua and Vis Acceleratrix:—
Those longnebbed words that to our text books still
Cling by their titles,
And from them creep, as entozoa will,
Into our vitals.
But see! Tait writes in lucid symbols clear
One small equation;
And Force becomes of Energy a mere
Spacevariation.
Ready to put on
Meanings most strange and various, fit to shock
Pupils of Newton....
The phrases of last century in this
Linger to play tricks—
Vis viva and Vis Mortua and Vis Acceleratrix:—
Those longnebbed words that to our text books still
Cling by their titles,
And from them creep, as entozoa will,
Into our vitals.
But see! Tait writes in lucid symbols clear
One small equation;
And Force becomes of Energy a mere
Spacevariation.
In despair, I offer your readers their choice of the following definitions of entropy. My authorities are such books and journals as I have by me at the moment.
(a) Entropy is that portion of the intrinsic energy of a system which cannot be converted into work by even a perfect heat engine.—Clausius.
(b) Entropy is that portion of the intrinsic energy which can be converted into work by a perfect engine.—Maxwell, following Tait.
(c) Entropy is that portion of the intrinsic energy which is not converted into work by our imperfect engines.—Swinburne.
(d) Entropy (in a volume of gas) is that which remains constant when heat neither enters nor leaves the gas.—W. Robinson.
(e) Entropy may be called the ‘thermal weight’, temperature being called the ‘thermal height.’—Ibid.
(f) Entropy is one of the factors of heat, temperature being the other.—Engineering.
I set up these bald statement as so many Aunt Sallys, for any one to shy at.
[Lamenting a list of confused interpretations of the meaning of entropy, being hotly debated in journals at the time.]
(a) Entropy is that portion of the intrinsic energy of a system which cannot be converted into work by even a perfect heat engine.—Clausius.
(b) Entropy is that portion of the intrinsic energy which can be converted into work by a perfect engine.—Maxwell, following Tait.
(c) Entropy is that portion of the intrinsic energy which is not converted into work by our imperfect engines.—Swinburne.
(d) Entropy (in a volume of gas) is that which remains constant when heat neither enters nor leaves the gas.—W. Robinson.
(e) Entropy may be called the ‘thermal weight’, temperature being called the ‘thermal height.’—Ibid.
(f) Entropy is one of the factors of heat, temperature being the other.—Engineering.
I set up these bald statement as so many Aunt Sallys, for any one to shy at.
[Lamenting a list of confused interpretations of the meaning of entropy, being hotly debated in journals at the time.]
Tait once urged the advantage of Quaternions on Cayley (who never used them), saying: “You know Quaternions are just like a pocketmap.” “That may be,” replied Cayley, “but you’ve got to take it out of your pocket, and unfold it, before it’s of any use.” And he dismissed the subject with a smile.
Tait dubbed Maxwell dp/dt, for according to thermodynamics dp/dt = JCM (where C denotes Carnot’s function) the initials of (J.C.) Maxwell’s name. On the other hand Maxwell denoted Thomson by T and Tait by T'; so that it became customary to quote Thomson and Tait’s Treatise on Natural Philosophy as T and T'.
In future times Tait will be best known for his work in the quaternion analysis. Had it not been for his expositions, developments and applications, Hamilton’s invention would be today, in all probability, a mathematical curiosity.
See also:
 28 Apr  short biography, births, deaths and events on date of Tait's birth.
 Life and Scientific Work of Peter Guthrie Tait, by Cargill Gilson Knott.  book suggestion.
 BooklistBooks by Peter Guthrie Tait.