Chapter 9, Problem 9.44P

Why is the boiling point of $\text{propane-1, 3-diol}$ $\left({\text{HOCH}}_{\text{2}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}\text{OH}\right)$ higher than the boiling point of

$\text{propane-1, 2-diol}$ $\left[{\text{HOCH}}_{\text{2}}\text{CH}\left(\text{OH}\right){\text{CH}}_{\text{3}}\right]$ ( $\text{215}\text{°C}$ vs. $\text{187}\text{°C}$)? Why do both diols have a higher

boiling point than $\text{butane-1-ol}$ ( $\left({\text{CH}}_3{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}\text{OH, 118}\text{°C}\right)$?