The Tine distribution (sometimes called symmetric triangular distribution) made an entry in the Index to the Distributions of Mathematical Statistics  as:
The Annals of Mathematical Statistics  contains an expanded definition:
Rinne  defines Tine’s distribution as the distribution of two independent and identically distributed uniform variables (i.e., the convolution of two uniform distributions):
X1, X2 iid∼ UN(a, b) ⇒ X = X1 + X2 ∼ TS(2 a + b, b).
He notes it is also called Simpson’s distribution, after Thomas Simpson (1710-1761) who is thought to be the first to suggest the distribution.
 Schmidt, R. Statistical Analysis of One-Dimensional Distributions. Annals of Mathematical Statistics. 5:33.
 Haight, F. (1958). Index to the Distributions of Mathematical Statistics. National Bureau of Standards Report.
 Rinne, H. Location–Scale Distributions Linear Estimation and Probability Plotting Using MATLAB. Online: http://geb.uni-giessen.de/geb/volltexte/2010/7607/pdf/RinneHorst_LocationScale_2010.pdf